Context initialization based on decoder picture buffer

ABSTRACT

A method for decoding a video frame includes receiving a slice in a video decoder, identifying the slice as one of at least a first predicted slice and a second predicted slice, receiving information used to determine a context initialization method corresponding to the slice, and initializing, based on the received information, one of a first context initialization method and a second context initialization method associated with the slice, and decoding the video frame using the slice and one of the first context initialization method and the second context initialization method. The first context initialization method is a method for initializing a context associated with the first predicted slice and the second context initialization method is a method for initializing a context associated with the second predicted slice.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to video codingand, in particular, some embodiments of the present invention relate totechniques for context initialization.

BACKGROUND

State-of-the-art video-coding methods and standards, for example,H.264/MPEG-4 AVC (H.264/AVC) and JCT-VC Test Model under Consideration(TMuC), may provide higher coding efficiency than older methods andstandards at the expense of higher complexity. Increasing qualityrequirements and resolution requirements on video coding methods andstandards may also increase their complexity. Decoders that supportparallel decoding may improve decoding speeds and reduce memoryrequirements. Additionally, advances in multi-core processors may makeencoders and decoders that support parallel decoding desirable.

H.264/MPEG-4 AVC [Joint Video Team of ITU-T VCEG and ISO/IEC MPEG,“H.264: Advanced video coding for generic audiovisual services,” ITU-TRec. H.264 and ISO/IEC 14496-10 (MPEG4—Part 10), November 2007], whichis hereby incorporated by reference herein in its entirety, is a videocodec (coder/decoder) specification that uses macroblock predictionfollowed by residual coding to reduce temporal and spatial redundancy ina video sequence for compression efficiency.

Test Model under Consideration (TMuC) [JCT-VC A205, “Test Model underConsideration,” Jun. 16, 2010], which is hereby incorporated byreference herein in its entirety, is the initial test model of JCT-VC.TMuC, using a basic coding unit called a coding tree block (CTB) thatcan have variable sizes, may provide more flexibility than H.264/AVC.

SUMMARY

Some embodiments of the present invention comprise methods and systemsfor parallel entropy encoding. Some embodiments of the present inventioncomprise methods and systems for parallel entropy decoding.

In some embodiments of the present invention, a scan pattern may beinitialized at the start of an entropy slice.

In some embodiments of the present invention, a scan pattern may beinitialized at a starting elementary unit in a row in an entropy slice.

In some embodiments of the present invention, a state associated with anadaptive scan calculation may be initialized at the start of an entropyslice.

In some embodiments of the present invention, a state associated with anadaptive scan calculation may be initialized at a starting elementaryunit in a row in an entropy slice.

In some embodiments of the present invention, a coefficient scanningorder may be decoupled from a context fetch order.

In some embodiments of the present invention, a forward-predictedB-slice may be detected and a context associated with entropy coding theforward-predicted B-slice may be initialized according to a P-slicemethod.

In some embodiments of the present invention, a context may beinitialized based on bin count.

In some embodiments of the present invention, a context may beinitialized based on quantization parameter value.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS

FIG. 1 is a picture showing an H.264/AVC video encoder (prior art);

FIG. 2 is a picture showing an H.264/AVC video decoder (prior art);

FIG. 3 is a picture showing an exemplary slice structure (prior art);

FIG. 4 is a picture showing an exemplary slice group structure (priorart);

FIG. 5 is a picture showing an exemplary slice partition according toembodiments of the present invention, wherein a picture may bepartitioned in at least one reconstruction slice and a reconstructionslice may be partitioned into more than one entropy slice;

FIG. 6 is chart showing exemplary embodiments of the present inventioncomprising an entropy slice;

FIG. 7 is a chart showing exemplary embodiments of the present inventioncomprising parallel entropy decoding of multiple entropy slices followedby slice reconstruction;

FIG. 8 is a chart showing exemplary embodiments of the present inventioncomprising prediction data/residual data multiplexing at the picturelevel for entropy slice construction;

FIG. 9 is a chart showing exemplary embodiments of the present inventioncomprising color-plane multiplexing at the picture level for entropyslice construction;

FIG. 10 is a chart showing exemplary embodiments of the presentinvention comprising trans-coding a bitstream by entropy decoding,forming entropy slices and entropy encoding;

FIG. 11 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein the number of bins associated witheach entropy slice in the plurality of entropy slices does not exceed apredefined number of bins;

FIG. 12 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein bins may be associated with anentropy slice until the number of bins in the entropy slice exceeds athreshold based on a predefined maximum number of bins;

FIG. 13 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein the number of bins associated witheach entropy slice in the plurality of entropy slices does not exceed apredefined number of bins and each reconstruction slice contains no morethan a predefined number of macroblocks;

FIG. 14 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein bins may be associated with anentropy slice until the number of bins in the entropy slice exceeds athreshold based on a predefined maximum number of bins and eachreconstruction slice contains no more than a predefined number ofmacroblocks;

FIG. 15 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein the number of bits associated witheach entropy slice in the plurality of entropy slices does not exceed apredefined number of bits;

FIG. 16 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein bits may be associated with anentropy slice until the number of bits in the entropy slices exceeds athreshold based on a predefined maximum number of bits;

FIG. 17 is a picture depicting exemplary embodiments of the presentinvention comprising multiple bin coders;

FIG. 18 is a picture depicting exemplary embodiments of the presentinvention comprising multiple context-adaptation units;

FIG. 19 is a picture depicting exemplary embodiments of the presentinvention comprising multiple bin coders and multiple context-adaptationunits;

FIG. 20 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein the size of an entropy slice isrestricted to limit the number of bins operated on, in the entropyslice, by each restricted entropy-coder unit;

FIG. 21 is a chart showing exemplary embodiments of the presentinvention comprising partitioning a reconstruction slice into aplurality of entropy slices, wherein the size of an entropy slice isrestricted to limit the number of bins operated on, in the entropyslice, by each restricted entropy-coder unit;

FIG. 22 is a picture depicting exemplary embodiments of the presentinvention comprising a plurality of bin decoders;

FIG. 23 is a picture depicting exemplary embodiments of the presentinvention comprising a plurality of context-adaptation units;

FIG. 24 is a picture depicting exemplary embodiments of the presentinvention comprising multiple bin decoders and multiplecontext-adaptation units;

FIG. 25 is a picture showing an exemplary partition of a reconstructionblock into a plurality of entropy slices in which the macroblocks withinan entropy slice are contiguous;

FIG. 26 is a picture showing an exemplary partition of a reconstructionblock into a plurality of entropy slices in which the macroblocks withinan entropy slice are not contiguous;

FIG. 27 is a picture illustrating non-contiguous neighboring blocks,used in entropy decoding, for an exemplary partition of a reconstructionblock into a plurality of entropy slices in which the macroblocks withinan entropy slice are not contiguous;

FIG. 28 is a picture illustrating neighboring blocks used in entropydecoding and reconstruction of a block within an entropy slice for anexemplary partition of a reconstruction block into a plurality ofentropy slice in which the macroblocks within an entropy slice are notcontiguous;

FIG. 29 is a pictorial representation of an exemplary portion of anexemplary bitstream depicting entropy-slice header locationrestrictions;

FIG. 30 is a pictorial representation of an exemplary portion of anexemplary bitstream depicting entropy-slice header locationrestrictions;

FIG. 31 is a chart showing exemplary embodiments of the presentinvention comprising an entropy decoder processing a restricted portionof a bitstream to identify an entropy-slice header;

FIG. 32 is a chart showing exemplary embodiments of the presentinvention comprising an entropy decoder processing a restricted portionof a bitstream to identify an entropy-slice header;

FIG. 33 is a chart showing exemplary embodiments of the presentinvention comprising an entropy decoder processing a restricted portionof a bitstream to identify an entropy-slice header;

FIG. 34 is a picture illustrating an exemplary context tableinitialization scheme within entropy slices according to embodiments ofthe present invention;

FIG. 35 is a chart showing exemplary embodiments of the presentinvention comprising an entropy encoder with context fetching decoupledfrom coefficient scan order;

FIG. 36 is a chart showing exemplary embodiments of the presentinvention comprising an entropy decoder with context fetching decoupledfrom coefficient scan order;

FIG. 37 is a chart showing exemplary embodiments of the presentinvention comprising bin-count-based context adaptation;

FIG. 38 is a picture illustrating an exemplary, disjoint partitioning ofa number of bins processed; and

FIG. 39 is a chart showing exemplary embodiments of the presentinvention comprising quantization-parameter-based context adaptation.

FIG. 40 illustrates an initialization technique.

FIG. 41 illustrates another initialization technique.

FIG. 42 illustrates an initialization technique.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present invention will be best understood byreference to the drawings, wherein like parts are designated by likenumerals throughout. The figures listed above are expressly incorporatedas part of this detailed description.

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the methods and systems of the present invention is notintended to limit the scope of the invention, but it is merelyrepresentative of the presently preferred embodiments of the invention.

Elements of embodiments of the present invention may be embodied inhardware, firmware and/or software. While exemplary embodiments revealedherein may only describe one of these forms, it is to be understood thatone skilled in the art would be able to effectuate these elements in anyof these forms while resting within the scope of the present invention.

While any video coder/decoder (codec) that uses entropyencoding/decoding may be accommodated by embodiments of the presentinvention, many exemplary embodiments of the present invention will beillustrated in relation to an H.264/AVC encoder and an H.264/AVCdecoder. This is intended for illustration of embodiments of the presentinvention and not as a limitation.

Many exemplary embodiments of the present invention may be described inrelation to a macroblock as an elementary unit. This is intended forillustration and not as a limitation.

U.S. patent application Ser. No. 12/058,301, entitled “Methods andSystems for Parallel Video Encoding and Decoding,” filed on Mar. 28,2008, is hereby incorporated by reference herein, in its entirety. U.S.patent application Ser. No. 12/579,236, entitled “Methods and Systemsfor Parallel Video Encoding and Decoding,” filed on Oct. 14, 2009, ishereby incorporated by reference herein, in its entirety.

State-of-the-art video-coding methods and standards, for example,H.264/AVC and TMuC, may provide higher coding efficiency than oldermethods and standards at the expense of higher complexity. Increasingquality requirements and resolution requirements on video coding methodsand standards may also increase their complexity. Decoders that supportparallel decoding may improve decoding speeds and reduce memoryrequirements. Additionally, advances in multi-core processors may makeencoders and decoders that support parallel decoding desirable.

H.264/AVC, and many other video coding standards and methods, are basedon a block-based hybrid video-coding approach, wherein the source-codingalgorithm is a hybrid of inter-picture, also considered inter-frame,prediction, intra-picture, also considered intra-frame, prediction andtransform coding of a prediction residual. Inter-frame prediction mayexploit temporal redundancies, and intra-frame and transform coding ofthe prediction residual may exploit spatial redundancies.

FIG. 1 shows a block diagram of an exemplary H.264/AVC video encoder 2.An input picture 4, also considered a frame, may be presented forencoding. A predicted signal 6 and a residual signal 8 may be produced,wherein the predicted signal 6 may be based on either an inter-frameprediction 10 or an intra-frame prediction 12. The inter-frameprediction 10 may be determined by motion compensating 14 a stored,reference picture 16, also considered reference frame, using motioninformation 19 determined by a motion estimation 18 process between theinput frame 4 and the reference frame 16. The intra-frame prediction 12may be determined 20 using a decoded signal 22. The residual signal 8may be determined by subtracting the input 4 from the prediction 6. Theresidual signal 8 is transformed, scaled and quantized 24, therebyproducing quantized, transform coefficients 26. The decoded signal 22may be generated by adding the predicted signal 6 to a signal 28generated by inverse transforming, scaling and inverse quantizing 30 thequantized, transform coefficients 26. The motion information 19 and thequantized, transform coefficients 26 may be entropy coded 32 and writtento the compressed-video bitstream 34. An output image region 38, forexample a portion of the reference frame, may be generated at theencoder 2 by filtering 36 the reconstructed, pre-filtered signal 22.

FIG. 2 shows a block diagram of an exemplary H.264/AVC video decoder 50.An input signal 52, also considered a bitstream, may be presented fordecoding. Received symbols may be entropy decoded 54, thereby producingmotion information 56 and quantized, scaled, transform coefficients 58.The motion information 56 may be used, with a portion of a referenceframe 65 which may reside in frame memory 64, to provide motioncompensation 60 for the H.264/AVC video decoder 50, and an inter-frameprediction 68 may be generated. The quantized, scaled, transformcoefficients 58 may be inverse quantized, scaled and inverse transformed62, thereby producing a decoded residual signal 70. The residual signal70 may be added to a prediction signal: either the inter-frameprediction signal 68 or an intra-frame prediction signal 76. Theintra-frame prediction signal 76 may be predicted 74 from previouslydecoded information in the current frame 72. The combined signal 72 maybe filtered 80 and the filtered signal 82 may be written to frame memory64.

In H.264/AVC, an input picture is partitioned into fixed-sizemacroblocks, wherein each macroblock covers a rectangular picture areaof 16×16 samples of the luma component and 8×8 samples of each of thetwo chroma components. In other codecs and standards, an elementaryunit, or basic coding unit, different than a macroblock, for example, acoding tree block, may be used. The decoding process of the H.264/AVCstandard is specified for processing units which are macroblocks. Theentropy decoder 54 parses the syntax elements of the compressed-videobitstream 52 and de-multiplexes them. H.264/AVC specifies twoalternative methods of entropy decoding: a low-complexity technique thatis based on the usage of context-adaptively switched sets of variablelength codes, referred to as CAVLC, and the computationally moredemanding algorithm of context-based adaptively binary arithmeticcoding, referred to as CABAC. In both entropy decoding methods, decodingof a current symbol may rely on previously, correctly decoded symbolsand adaptively updated context models. In addition, different datainformation, for example, prediction data information, residual datainformation and different color planes, may be multiplexed together.De-multiplexing may not be done until elements are entropy decoded.

After entropy decoding, a macroblock may be reconstructed by obtaining:the residual signal through inverse quantization and the inversetransform, and the prediction signal, either the intra-frame predictionsignal or the inter-frame prediction signal. Blocking distortion may bereduced by applying a de-blocking filter to every decoded macroblock. Noprocessing may begin until the input signal is entropy decoded, therebymaking entropy decoding a potential bottleneck in decoding.

Similarly, in codecs in which alternative prediction mechanisms may beallowed, for example, inter-layer prediction in H.264/AVC or inter-layerprediction in other scalable codecs, entropy decoding may be requisiteprior to all processing at the decoder, thereby making entropy decodinga potential bottleneck.

In H.264/AVC, an input picture comprising a plurality of macroblocks maybe partitioned into one or several slices. The values of the samples inthe area of the picture that a slice represents may be correctly decodedwithout the use of data from other slices provided that the referencepictures used at the encoder and the decoder are identical. Therefore,entropy decoding and macroblock reconstruction for a slice do not dependon other slices. In particular, the entropy coding state is reset at thestart of each slice. The data in other slices are marked as unavailablewhen defining neighborhood availability for both entropy decoding andreconstruction. In H.264/AVC, slices may be entropy decoded andreconstructed in parallel. No intra prediction and motion-vectorprediction are allowed across the slice boundary. De-blocking filteringmay use information across slice boundaries.

FIG. 3 shows an exemplary video picture 90 comprising eleven macroblocksin the horizontal direction and nine macroblocks in the verticaldirection (nine exemplary macroblocks labeled 91-99). FIG. 3 shows threeexemplary slices: a first slice denoted “SLICE #0” 100, a second slicedenoted “SLICE #1” 101 and a third slice denoted “SLICE #2” 102. AnH.264/AVC decoder may decode and reconstruct the three slices 100, 101,102 in parallel. At the beginning of the decoding/reconstruction processfor each slice, context models are initialized or reset and macroblocksin other slices are marked as unavailable for both entropy decoding andmacroblock reconstruction. Thus, for a macroblock, for example, themacroblock labeled 93, in “SLICE #1,” macroblocks (for example,macroblocks labeled 91 and 92) in “SLICE #0” may not be used for contextmodel selection or reconstruction. Whereas, for a macroblock, forexample, the macroblock labeled 95, in “SLICE #1,” other macroblocks(for example, macroblocks labeled 93 and 94) in “SLICE #1” may be usedfor context model selection or reconstruction. Therefore, entropydecoding and macroblock reconstruction must proceed serially within aslice. Unless slices are defined using flexible macroblock ordering(FMO), macroblocks within a slice are processed in the order of a rasterscan.

Flexible macroblock ordering defines a slice group to modify how apicture is partitioned into slices. The macroblocks in a slice group aredefined by a macroblock-to-slice-group map, which is signaled by thecontent of the picture parameter set and additional information in theslice headers. The macroblock-to-slice-group map consists of aslice-group identification number for each macroblock in the picture.The slice-group identification number specifies to which slice group theassociated macroblock belongs. Each slice group may be partitioned intoone or more slices, wherein a slice is a sequence of macroblocks withinthe same slice group that is processed in the order of a raster scanwithin the set of macroblocks of a particular slice group. Entropydecoding and macroblock reconstruction must proceed serially within aslice.

FIG. 4 depicts an exemplary macroblock allocation into three slicegroups: a first slice group denoted “SLICE GROUP #0” 103, a second slicegroup denoted “SLICE GROUP #1” 104 and a third slice group denoted“SLICE GROUP #2” 105. These slice groups 103, 104, 105 may be associatedwith two foreground regions and a background region, respectively, inthe picture 90.

Some embodiments of the present invention may comprise partitioning apicture into one or more reconstruction slices, wherein a reconstructionslice may be self-contained in the respect that values of the samples inthe area of the picture that the reconstruction slice represents may becorrectly reconstructed without use of data from other reconstructionslices, provided that the references pictures used are identical at theencoder and the decoder. All reconstructed macroblocks within areconstruction slice may be available in the neighborhood definition forreconstruction.

Some embodiments of the present invention may comprise partitioning areconstruction slice into more than one entropy slice, wherein anentropy slice may be self-contained in the respect that symbol values inthe area of the picture that the entropy slice represents may becorrectly entropy decoded without the use of data from other entropyslices. In some embodiments of the present invention, the entropy codingstate may be reset at the decoding start of each entropy slice. In someembodiments of the present invention, the data in other entropy slicesmay be marked as unavailable when defining neighborhood availability forentropy decoding. In some embodiments of the present invention,macroblocks in other entropy slices may not be used in a current block'scontext model selection. In some embodiments of the present invention,the context models may be updated only within an entropy slice. In theseembodiments of the present invention, each entropy decoder associatedwith an entropy slice may maintain its own set of context models.

ITU Telecommunication Standardization Sector, Study Group16—Contribution 405 entitled “Entropy slices for parallel entropydecoding,” April 2008, is hereby incorporated by reference herein in itsentirety.

Some embodiments of the present invention may comprise CABACencoding/decoding. The CABAC encoding process includes the followingfour elementary steps: binarization; context model selection; binaryarithmetic coding; and probability update.

Binarization:

A non-binary-valued symbol (for example, a transform coefficient, amotion vector, or other coding data) is converted into a binary code,also referred to as a bin string or a binarized symbol. When abinary-valued syntax element is given, the initial step of binarizationmay be bypassed. A binary-valued syntax element or an element of abinarized symbol may be referred to as a bin.

For each bin, the following may be performed:

Context Model Selection:

A context model is a probability model for one or more bins. The contextmodel comprises, for each bin, the probability of the bin being a “1” ora “0.” The model may be chosen for a selection of available modelsdepending on the statistics of recently coded data symbols, usuallybased on the left and above neighboring symbols, if available.

Binary Arithmetic Coding:

An arithmetic coder encodes each bin according to the selectedprobability model and is based on recursive interval subdivision.

Probability Update:

The selected context model is updated based on the actual coded value.

Context adaptation may refer to the process of selecting, based onneighboring symbol values, a context model state, also referred to as astate, associated with a bin and updating a model probabilitydistribution assigned to the given symbols. The location of theneighboring symbols may be defined according to a context template.

In some embodiments of the present invention comprising CABACencoding/decoding, at the decoding start of an entropy slice, all of thecontext models may be initialized or reset to predefined models.

Some embodiments of the present invention may be understood in relationto FIG. 5. FIG. 5 shows an exemplary video frame 110 comprising elevenmacroblocks in the horizontal direction and nine macroblocks in thevertical direction (nine exemplary macroblocks in frames labeled 117,118, 119, 120, 121, 122, 123, 124, and 125). FIG. 5 shows threeexemplary reconstruction slices: a first reconstruction slice denoted“R_SLICE #0” 111, a second reconstruction slice denoted “R_SLICE #1” 112and a third reconstruction slice denoted “R_SLICE #2” 113. FIG. 5further shows a partitioning of the second reconstruction slice “R_SLICE#1” 112 into three entropy slices: a first entropy slice denoted“E_SLICE #0” shown in cross-hatch 114, a second entropy slice denoted“E_SLICE #1” shown in vertical-hatch 115 and a third entropy slicedenoted “E_SLICE #2” shown in angle-hatch 116. Each entropy slice 114,115, 116 may be entropy decoded in parallel.

In some embodiments of the present invention, only data from macroblockswithin an entropy slice may be available for context model selectionduring entropy decoding of the entropy slice. All other macroblocks maybe marked as unavailable. For this exemplary partitioning, themacroblocks in frames labeled 119 and 120 are unavailable for contextmodel selection when decoding symbols corresponding to the area of themacroblock in the frame labeled 121 because the macroblocks in frameslabeled 119 and 120 are outside of the entropy slice containing themacroblock in the frame labeled 121. However, these macroblocks inframes 119 and 120 are available when the macroblock in the framelabeled 121 is reconstructed.

In some embodiments of the present invention, an encoder may determinewhether or not to partition a reconstruction slice into entropy slices,and the encoder may signal the decision in the bitstream. In someembodiments of the present invention, the signal may comprise anentropy-slice flag, which may be denoted “entropy_slice_flag” in someembodiments of the present invention.

Some decoder embodiments of the present invention may be described inrelation to FIG. 6. In these embodiments, an entropy-slice flag may beexamined 130, and if the entropy-slice flag indicates that there are no132 entropy slices associated with a picture, or a reconstruction slice,then the header may be parsed 134 as a regular slice header. The entropydecoder state may be reset 136, and the neighbor information for theentropy decoding and the reconstruction may be defined 138. The slicedata may then be entropy decoded 140, and the slice may be reconstructed142. If the entropy-slice flag indicates there are 146 entropy slicesassociated with a picture, or a reconstruction slice, then the headermay be parsed 148 as an entropy-slice header. The entropy decoder statemay be reset 150, the neighbor information for entropy decoding may bedefined 152 and the entropy-slice data may be entropy decoded 154. Theneighbor information for reconstruction may then be defined 156, and theslice may be reconstructed 142. After slice reconstruction 142, the nextslice, or picture, may be examined 158.

Some alternative decoder embodiments of the present invention may bedescribed in relation to FIG. 7. In these embodiments, the decoder maybe capable of parallel decoding and may define its own degree ofparallelism, for example, consider a decoder comprising the capabilityof decoding N entropy slices in parallel. The decoder may identify 170 Nentropy slices. In some embodiments of the present invention, if fewerthan N entropy slices are available in the current picture, orreconstruction slice, the decoder may decode entropy slices fromsubsequent pictures, or reconstruction slices, if they are available. Inalternative embodiments, the decoder may wait until the current picture,or reconstruction slice, is completely processed before decodingportions of a subsequent picture, or reconstruction slice. Afteridentifying 170 up to N entropy slices, each of the identified entropyslices may be independently entropy decoded. A first entropy slice maybe decoded 172-176. The decoding 172-176 of the first entropy slice maycomprise resetting the decoder state 172. In some embodiments comprisingCABAC entropy decoding, the CABAC state may be reset. The neighborinformation for the entropy decoding of the first entropy slice may bedefined 174, and the first entropy slice data may be decoded 176. Foreach of the up to N entropy slices, these steps may be performed(178-182 for the Nth entropy slice). In some embodiments of the presentinvention, the decoder may reconstruct 184 the entropy slices when allof the entropy slices are entropy decoded. In alternative embodiments ofthe present invention, the decoder may begin reconstruction 184 afterone or more entropy slices are decoded.

In some embodiments of the present invention, when there are more than Nentropy slices, a decode thread may begin entropy decoding a nextentropy slice upon the completion of entropy decoding of an entropyslice. Thus when a thread finishes entropy decoding a low complexityentropy slice, the thread may commence decoding additional entropyslices without waiting for other threads to finish their decoding.

In some embodiments of the present invention which may accommodate anexisting standard or method, an entropy slice may share most of theslice attributes of a regular slice according to the standard or method.Therefore, an entropy slice may require a small header. In someembodiments of the present invention, the entropy slice header may allowa decoder to identify the start of an entropy slice and start entropydecoding. In some embodiments, at the start of a picture, or areconstruction slice, the entropy slice header may be the regularheader, or a reconstruction slice header.

In some embodiments of the present invention comprising an H.264/AVCcodec, an entropy slice may be signaled by adding a new bit,“entropy_slice_flag” to the existing slice header. Table 1 lists thesyntax for an entropy slice header according to embodiments of thepresent invention, wherein C indicates Category and Descriptor u(1),ue(v) indicate some fixed length or variable length coding methods.Embodiments of the present invention comprising an “entropy_slice_flag”may realize improved coding efficiency.

“first_mb_in_slice” specifies the address of the first macroblock in theentropy slice associated with the entropy-slice header. In someembodiments, the entropy slice may comprise a sequence of macroblocks.

“cabac_init_idc” specifies the index for determining the initializationtable used in the initialization process for the context model.

TABLE 1 Exemplary Syntax Table for Entropy Slice Header slice_header( ){ C Descriptor  entropy_slice_flag 2 u(1)  if (entropy_slice_flag) {  first_mb_in_slice 2 ue(v)   if (entropy_coding_mode_flag &&  slice_type != I && slice_type != SI)    cabac_init_idc 2 ue(v)   }  } else {   a regular slice header ...  } }

In some embodiments of the present invention, an entropy slice may beassigned a different network abstraction layer (NAL) unit type from theregular slices. In these embodiments, a decoder may distinguish betweenregular slices and entropy slices based on the NAL unit type. In theseembodiments, the bit field “entropy_slice_flag” is not required.

In some embodiments of the present invention, the bit field“entropy_slice_flag” may not be transmitted in all profiles. In someembodiments of the present invention, the bit field “entropy_slice_flag”may not be transmitted in a baseline profile, but the bit field“entropy_slice_flag” may be transmitted in higher profiles such as amain, an extended or a professional profile. In some embodiments of thepresent invention, the bit field “entropy_slice_flag” may only betransmitted in bitstreams associated with characteristics greater than afixed characteristic value. Exemplary characteristics may includespatial resolution, frame rate, bit depth, bit rate and other bitstreamcharacteristics. In some embodiments of the present invention, the bitfield “entropy_slice_flag” may only be transmitted in bitstreamsassociated with spatial resolutions greater than 1920×1080 interlaced.In some embodiments of the present invention, the bit field“entropy_slice_flag” may only be transmitted in bitstreams associatedwith spatial resolutions greater than 1920×1080 progressive. In someembodiments of the present invention, if the bit field“entropy_slice_flag” is not transmitted, a default value may be used.

In some embodiments of the present invention, an entropy slice may beconstructed by altering the data multiplexing. In some embodiments ofthe present invention, the group of symbols contained in an entropyslice may be multiplexed at the macroblock level. In alternativeembodiments of the present invention, the group of symbols contained inan entropy slice may be multiplexed at the picture level. In otheralternative embodiments of the present invention, the group of symbolscontained in an entropy slice may be multiplexed by data type. In yetalternative embodiments of the present invention, the group of symbolscontained in an entropy slice may be multiplexed in a combination of theabove.

Some embodiments of the present invention comprising entropy sliceconstruction based on picture level multiplexing may be understood inrelation to FIG. 8 and FIG. 9. In some embodiments of the presentinvention shown in FIG. 8, prediction data 190 and residual data 192 maybe entropy encoded 194, 196 separately and multiplexed 198 at thepicture level. In some embodiments of the present invention, theprediction data for a picture 190 may be associated with a first entropyslice, and the residual data for a picture 192 may be associated with asecond entropy slice. The encoded prediction data and the encodedentropy data may be decoded in parallel. In some embodiments of thepresent invention, each partition comprising prediction data or residualdata may be partitioned into entropy slices which may be decoded inparallel.

In some embodiments of the present invention shown in FIG. 9, theresidual of each color plane, for example, the luma residual 200 and thetwo chroma residuals 202, 204, may be entropy encoded 206, 208, 210separately and multiplexed 212 at the picture level. In some embodimentsof the present invention, the luma residual for a picture 200 may beassociated with a first entropy slice, the first chroma residual for apicture 202 may be associated with a second entropy slice, and thesecond residual for a picture 204 may be associated with a third entropyslice. The encoded residual data for the three color planes may bedecoded in parallel. In some embodiments of the present invention, eachpartition comprising color-plane residual data may be partitioned intoentropy slices which may be decoded in parallel. In some embodiments ofthe present invention, the luma residual 200 may have relatively moreentropy slices compared to the chroma residuals 202, 204.

In some embodiments of the present invention, an compressed-videobitstream may be trans-coded to comprise entropy slices, therebyallowing for parallel entropy decoding as accommodated by embodiments ofthe present invention described above. Some embodiments of the presentinvention may be described in relation to FIG. 10. An input bitstreamwithout entropy slices may be processed picture-by-picture according toFIG. 10. In these embodiments of the present invention, a picture fromthe input bitstream may be entropy decoded 220. The data which had beencoded, for example, mode data, motion information, residual informationand other data, may be obtained. Entropy slices may be constructed 222one at a time from the data. An entropy-slice header corresponding to anentropy slice may be inserted 224 in a new bitstream. The encoder statemay be reset and the neighbor information defined 226. The entropy slicemay be entropy encoded 228 and written to the new bitstream. If there ispicture data that has not been consumed 232 by the constructed entropyslices, then another entropy slice may be constructed 222, and theprocess 224-230 may continue until all of the picture data has beenconsumed 234 by the constructed entropy slices, and then the nextpicture may be processed.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices wherein the sizeof each entropy slice may be less than, or may not exceed, a fixednumber of bins. In some embodiments wherein the encoder may restrict thesize of each entropy slice, the maximum number of bins may be signaledin the bitstream. In alternative embodiments wherein the encoder mayrestrict the size of each entropy slice, the maximum number of bins maybe defined by the profile and level conformance point of the encoder.For example, Annex A of the H.264/AVC video coding specification may beextended to comprise a definition of the maximum number of bins allowedin an entropy slice.

In some embodiments of the present invention, the maximum number of binsallowed in an entropy slice may be indicated for each level conformancepoint of the encoder according to a table, for example, as shown inTable 2, where M_(m.n) denotes the maximum number of bins allowed in anentropy slice for a level m.n conformance point.

TABLE 2 Maximum Number of Bins per Entropy Slice for Each Level MaximumNumber of Bins Level per Entropy Slice 1.1 M_(1.1) 1.2 M_(1.2) . . . . .. m.n M_(m.n) . . . . . . 5.1 M_(5.1)

Exemplary maximum number of bins allowed in an entropy slice areM_(1.1)=1,000 bins, M_(1.2)=2,000 bins, . . . , and M_(5.1)=40,000 bins.Other exemplary maximum number of bins allowed in an entropy slice areM_(1.1)=2,500 bins, M_(1.2)=4,200 bins, . . . , and M_(5.1)=150,000bins.

In some embodiments, a set of maximum number of bins allowed in anentropy slice may be determined for all levels based on bit rate, imagesize, number of macroblocks and other encoding parameters. In someembodiments of the present invention the maximum number of bins allowedin an entropy slice may be the set to the same number for all levels.Exemplary values are 38,000 bins and 120,000 bins.

In some embodiments of the present invention, an encoder may determine aworst case number of bins associated with a macroblock, and the encodermay write the bins associated with:

$\frac{ESLICE\_ MaxNumberBins}{BinsPerMB},$macroblocks to each entropy slice, where ESLICE_MaxNumberBins may denotethe maximum number of bins allowed in an entropy slice and BinsPerMB maydenote the worst case number of bins associated with a macroblock. Insome embodiments, the macroblocks may be selected in raster-scan order.In alternative embodiments, the macroblocks may be selected in another,predefined order. In some embodiments, the worst case number of binsassociated with a macroblock may be a fixed number. In alternativeembodiments, the encoder may update the worst case number based onmeasurements of the sizes of previously processed macroblocks.

Some embodiments of the present invention may be described in relationto FIG. 11. In these embodiments, an encoder may, for a reconstructionslice, partition the reconstruction slice into a plurality of entropyslices wherein no entropy slice may be larger in size than apredetermined number of bins. The encoder may initialize 240 to zero acounter associated with the number of bins in a current entropy slice.The counter value may be denoted A for illustrative purposes in theremainder of the description of the embodiments of the present inventiondescribed in relation to FIG. 11. The syntax elements for a nextmacroblock may be obtained 242. The next macroblock may be determinedaccording to a predefined macroblock processing order. In someembodiments, the macroblock processing order may correspond to araster-scan ordering. Non-binary syntax elements in the macroblock maybe converted 244 to a string of bins. Binary syntax elements may notrequire conversion. The number of bins associated with the macroblockmay be determined 246. The number of bins associated with the macroblockmay include the bins in the strings of bins associated with thenon-binary syntax elements in addition to the binary syntax elements,and the number of bins associated with the macroblock may be denoted numfor illustrative purposes in the remainder of the description of theembodiments of the present invention described in relation to FIG. 11.

If the number of bins associated with the macroblock may be added 248 tothe number of already accumulated bins associated with the currententropy slice without 249 exceeding a maximum number of bins allowed foran entropy slice, then the number of accumulated bins associated withthe current entropy slice may be updated 250 to include the binsassociated with the macroblock, and the bins associated with themacroblock may be written 252, by the entropy encoder, to the bitstreamand associated with the current entropy slice. The syntax elements forthe next macroblock may be obtained 242, and the partitioning processmay continue.

If the sum 248 of the number of bins associated with the macroblock andthe number of already accumulated bins associated with the currententropy slice exceeds 253 the maximum number of bins allowed for anentropy slice, then the encoder may start 254 a new entropy sliceassociated with the current reconstruction slice and may terminate thecurrent entropy slice. Then the counter associated with the number ofbins in the new, now current, entropy slice may be initialized 256 tozero. The number of accumulated bins associated with the current entropyslice may be updated 250 to include the bins associated with themacroblock, and the bins associated with the macroblock may be written252, by the entropy encoder, to the bitstream and associated with thecurrent entropy slice. The syntax elements for the next macroblock maybe obtained 242, and the partitioning process may continue.

Some embodiments of the present invention may be described in relationto FIG. 12. In these embodiments, an encoder may, for a reconstructionslice, partition the reconstruction slice into a plurality of entropyslices wherein no entropy slice may be larger in size than apredetermined maximum number of bins. In these embodiments, the encodermay associate macroblock syntax elements with an entropy slice until thesize of the entropy slice reaches a threshold associated with thepredetermined maximum number of bins allowed in an entropy slice. Insome embodiments, the threshold may be a percentage of the maximumnumber of bins allowed in an entropy slice. In one exemplary embodiment,the threshold may be 90% of the maximum number of bins allowed in anentropy slice, supposing that the greatest number of bins expected in amacroblock is less than 10% of the maximum number of bins. In anotherexemplary embodiment, the threshold may be a percentage of the maximumnumber of bins allowed in an entropy slice wherein the percentage may bebased on the greatest number of bins expected in a macroblock. In theseembodiments, once the size of an entropy slice exceeds a threshold size,then another entropy slice may be created. The threshold size may beselected to ensure that the entropy slice does not exceed the maximumnumber of bins allowed in an entropy slice. In some embodiments, thethreshold size may be a function of the maximum number of bins allowedin an entropy slice and an estimate of the maximum number of binsexpected for a macroblock.

The encoder may initialize 270 to zero a counter associated with thenumber of bins in a current entropy slice. The counter value may bedenoted A for illustrative purposes in the remainder of the descriptionof the embodiments of the present invention described in relation toFIG. 12. The syntax elements for a next macroblock may be obtained 272.The next macroblock may be determined according to a predefinedmacroblock processing order. In some embodiments, the macroblockprocessing order may correspond to a raster-scan ordering. Non-binarysyntax elements in the macroblock may be converted 274 to a string ofbins. Binary syntax elements may not require conversion. The binsassociated with the macroblock may be written 276, by the entropyencoder, to the bitstream and associated with the current entropy slice.The number of bins associated with the macroblock may be determined 278,and the number of accumulated bins associated with the current entropyslice may be updated 280 to include the bins associated with themacroblock. The number of accumulated bins associated with the currententropy slice is compared 282 with a threshold. If the number ofaccumulated bins associated with the current entropy slice is greaterthan the threshold, which may be denoted TH(MaxNumBins), based on themaximum number of bins allowed in an entropy slice 284, then the encodermay start 286 a new entropy slice and may terminate the current entropyslice. Then the encoder may initialize 288 to zero the counterassociated with the number of bins in the new, now current, entropyslice. The syntax elements for the next macroblock may be obtained 272,and the partitioning process may continue. If the number of accumulatedbins associated with the current entropy slice is not greater than thethreshold based on the maximum number of bins allowed in an entropyslice 283, then the syntax elements for the next macroblock may beobtained 272, and the partitioning process may continue.

In some embodiments of the present invention, an encoder may terminatethe current reconstruction slice and start a new reconstruction slicewhen a predetermined number of macroblocks have been assigned to thecurrent reconstruction slice.

Some embodiments of the present invention may be described in relationto FIG. 13. In these embodiments, an encoder may terminate the currentreconstruction slice and start a new reconstruction slice when apredetermined number of macroblocks have been assigned to the currentreconstruction slice. The encoder may initialize 300 to zero a counterassociated with the number of macroblocks in a current reconstructionslice. The counter value may be denoted AMB for illustrative purposes inthe remainder of the description of the embodiments of the presentinvention described in relation to FIG. 13. The encoder may initialize310 to zero a counter associated with the number of bins in a currententropy slice. The counter value may be denoted ABin for illustrativepurposes in the remainder of the description of the embodiments of thepresent invention described in relation to FIG. 13. The counter value ofthe counter associated with the number of macroblocks in the currentreconstruction slice is compared 312 with a predetermined maximum numberof macroblocks allowed in a reconstruction slice. If the counter valueof the counter associated with the number of macroblocks in the currentreconstruction slice is not less than the predetermined maximum numberof macroblocks allowed in a reconstruction slice 331, then a new entropyslice may be started 332 and a new reconstruction slice may be started334, terminating the current reconstruction slice and current entropyslice. The maximum number of macroblocks allowed in a reconstructionslice may be denoted MaxMBperRSlice for illustrative purposes in theremainder of the description of the embodiments of the present inventiondescribed in relation to FIG. 13.

If the counter value of the counter associated with the number ofmacroblocks in the current reconstruction slice is less than thepredetermined maximum number of macroblocks allowed in a reconstructionslice 313, then the syntax elements for a next macroblock may beobtained 314. The next macroblock may be determined according to apredefined macroblock processing order. In some embodiments, themacroblock processing order may correspond to a raster-scan ordering.Non-binary syntax elements in the macroblock may be converted 316 to astring of bins. Binary syntax elements may not require conversion. Thenumber of bins associated with the macroblock may be determined 318. Thenumber of bins associated with the macroblock may include the bins inthe strings of bins associated with the non-binary syntax elements inaddition to the binary syntax elements, and the number of binsassociated with the macroblock may be denoted num for illustrativepurposes in the remainder of the description of the embodiments of thepresent invention described in relation to FIG. 13.

If the number of bins associated with the macroblock may be added 320 tothe number of already accumulated bins associated with the currententropy slice without 321 exceeding a maximum number of bins allowed foran entropy slice, then the number of accumulated bins associated withthe current entropy slice may be updated 322 to include the binsassociated with the macroblock, the bins associated with the macroblockmay be written 324, by the entropy encoder, to the bitstream andassociated with the current entropy slice, and the number of macroblocksassociated with the current reconstruction slice may be incremented 326.Preferably, the number of macroblocks associated with the currentreconstruction slice is incremented by 1. The number of macroblocksassociated with the current reconstruction slice may be compared 312 tothe predetermined maximum number of macroblocks allowed in areconstruction slice, and the partitioning process may continue.

If the sum 320 of the number of bins associated with the macroblock andthe number of already accumulated bins associated with the currententropy slice exceeds 327 the maximum number of bins allowed for anentropy slice, then the encoder may start 328 a new, now current,entropy slice associated with the current reconstruction slice, and thecounter associated with the number of bins in the current entropy slicemay be initialized 330 to zero. The number of accumulated binsassociated with the current entropy slice may be updated 322 to includethe bins associated with the macroblock, the bins associated with themacroblock may be written 324, by the entropy encoder, to the bitstreamand associated with the current entropy slice, and the number ofmacroblocks associated with the current reconstruction slice may beincremented 326. The number of macroblocks associated with the currentreconstruction slice may be compared 312 to the predetermined maximumnumber of macroblocks allowed in a reconstruction slice, and thepartitioning process may continue.

Some embodiments of the present invention may be described in relationto FIG. 14. In these embodiments, an encoder may start a newreconstruction slice when a predetermined number of macroblocks havebeen assigned to the current reconstruction slice. In these embodiments,the encoder may associate macroblock syntax elements with an entropyslice until the size of the entropy slice reaches a threshold associatedwith the predetermined maximum number of bins allowed in an entropyslice. In some embodiments, the threshold may be a percentage of themaximum number of bins allowed in an entropy slice. In one exemplaryembodiment, the threshold may be 90% of the maximum number of binsallowed in an entropy slice, supposing that the greatest number of binsexpected in a macroblock is less than 10% of the maximum number of bins.In another exemplary embodiment, the threshold may be a percentage ofthe maximum number of bins allowed in an entropy slice wherein thepercentage may be based on the greatest number of bins expected in amacroblock. In these embodiments, once the size of an entropy sliceexceeds a threshold size, then another entropy slice may be created. Thethreshold size may be selected to ensure that the entropy slice does notexceed the maximum number of bins allowed in an entropy slice. In someembodiments, the threshold size may be a function of the maximum numberof bins allowed in an entropy slice and an estimate of the maximumnumber of bins expected for a macroblock.

The encoder may initialize 350 to zero a counter associated with thenumber of macroblocks in a current reconstruction slice. The countervalue may be denoted AMB for illustrative purposes in the remainder ofthe description of the embodiments of the present invention described inrelation to FIG. 14. The encoder may initialize 352 to zero a counterassociated with the number of bins in a current entropy slice. Thecounter value may be denoted ABin for illustrative purposes in theremainder of the description of the embodiments of the present inventiondescribed in relation to FIG. 14. The counter value of the counterassociated with the number of macroblocks in the current reconstructionslice is compared 354 with a predetermined maximum number of macroblocksallowed in a reconstruction slice. If the counter value of the counterassociated with the number of macroblocks in the current reconstructionslice is not less than the predetermined maximum number of macroblocksallowed in a reconstruction slice 373, then a new entropy slice may bestarted 374, and a new reconstruction slice may be started 376. Themaximum number of macroblocks allowed in a reconstruction slice may bedenoted MaxMBperRSlice for illustrative purposes in the remainder of thedescription of the embodiments of the present invention described inrelation to FIG. 14.

If the counter value of the counter associated with the number ofmacroblocks in the current reconstruction slice is less than thepredetermined maximum number of macroblocks allowed in a reconstructionslice 355, then the syntax elements for a next macroblock may beobtained 356. The next macroblock may be determined according to apredefined macroblock processing order. In some embodiments, themacroblock processing order may correspond to a raster-scan ordering.Non-binary syntax elements in the macroblock may be converted 358 to astring of bins. Binary syntax elements may not require conversion. Thebins associated with the macroblock may be written 360, by the entropyencoder, to the bitstream and associated with the current entropy slice.The number of bins associated with the macroblock may be determined 362,and the number of accumulated bins associated with the current entropyslice may be updated 364 to include the bins associated with themacroblock. The number of accumulated bins associated with the currententropy slice is compared 366 with a threshold. If the number ofaccumulated bins associated with the current entropy slice is greaterthan the threshold, which may be denoted TH(MaxNumBins), based on themaximum number of bins allowed in an entropy slice 369, then the encodermay start 370 a new entropy slice, and initialize 372 to zero thecounter associated with the number of bins in a current entropy slice.The number of macroblocks associated with the current reconstructionslice may be incremented 368. The number of macroblocks associated withthe current reconstruction slice may be compared 354 to thepredetermined maximum number of macroblocks allowed in a reconstructionslice, and the partitioning process may continue. If the number ofaccumulated bins associated with the current entropy slice is notgreater than the threshold based on the maximum number of bins allowedin an entropy slice 367, then the number of macroblocks associated withthe current reconstruction slice may be incremented 368, and the numberof macroblocks associated with the current reconstruction slice may becompared 354 to the predetermined maximum number of macroblocks allowedin a reconstruction slice, and the partitioning process may continue.

In alternative embodiments of the present invention, an encoder maypartition a reconstruction slice into a plurality of entropy slices,wherein each entropy slice may be associated with no more than apredefined number of bits.

Some embodiments of the present invention may be described in relationto FIG. 15. In these embodiments, an encoder may, for a reconstructionslice, partition the reconstruction slice into a plurality of entropyslices wherein no entropy slice may be larger in size than apredetermined number of bits. The encoder may initialize 400 to zero acounter associated with the number of bits in a current entropy slice.The counter value may be denoted A for illustrative purposes in theremainder of the description of the embodiments of the present inventiondescribed in relation to FIG. 15. The syntax elements for a nextmacroblock may be obtained 402. The next macroblock may be determinedaccording to a predefined macroblock processing order. In someembodiments, the macroblock processing order may correspond to araster-scan ordering. Non-binary syntax elements in the macroblock maybe converted 404 to a string of bins. Binary syntax elements may notrequire conversion. The bins, converted non-binary elements and binaryelements, associated with the macroblock may be presented to the entropyencoder, and the bins may be entropy encoded 406. The number of bitsassociated with the macroblock may be determined 408. The number of bitsassociated with the macroblock may be denoted num for illustrativepurposes in the remainder of the description of the embodiments of thepresent invention described in relation to FIG. 15.

If the number of bits associated with the macroblock may be added 410 tothe number of already accumulated bits associated with the currententropy slice without 411 exceeding a maximum number of bits allowed foran entropy slice, then the number of accumulated bits associated withthe current entropy slice may be updated 412 to include the bitsassociated with the macroblock, and the bits associated with themacroblock may be written 414 to the bitstream and associated with thecurrent entropy slice. The syntax elements for the next macroblock maybe obtained 402, and the partitioning process may continue.

If the sum 410 of the number of bits associated with the macroblock andthe number of already accumulated bits associated with the currententropy slice exceeds 415 the maximum number of bits allowed for anentropy slice, then the encoder may start 416 a new entropy sliceassociated with the current reconstruction slice, and the counterassociated with the number of bits in the current entropy slice may beinitialized 418 to zero. The number of accumulated bits associated withthe current entropy slice may be updated 412 to include the bitsassociated with the macroblock, and the bits associated with themacroblock may be written 414 to the bitstream and associated with thecurrent entropy slice. The syntax elements for the next macroblock maybe obtained 402, and the partitioning process may continue.

Some embodiments of the present invention may be described in relationto FIG. 16. In these embodiments, an encoder may, for a reconstructionslice, partition the reconstruction slice into a plurality of entropyslices wherein no entropy slice may be larger in size than apredetermined maximum number of bits. In these embodiments, the encodermay associate macroblock syntax elements with an entropy slice until thesize of the entropy slice reaches a threshold associated with thepredetermined maximum number of bits allowed in an entropy slice. Insome embodiments, the threshold may be a percentage of the maximumnumber of bits allowed in an entropy slice. In one exemplary embodiment,the threshold may be 90% of the maximum number of bits allowed in anentropy slice, supposing that the greatest number of bits expected in amacroblock is less than 10% of the maximum number of bits. In anotherexemplary embodiment, the threshold may be a percentage of the maximumnumber of bits allowed in an entropy slice wherein the percentage may bebased on the greatest number of bits expected in a macroblock. In theseembodiments, once the size of an entropy slice exceeds a threshold size,then another entropy slice may be created. The threshold size may beselected to ensure that the entropy slice does not exceed the maximumnumber of bits allowed in an entropy slice. In some embodiments, thethreshold size may be a function of the maximum number of bits allowedin an entropy slice and an estimate of the maximum number of bitsexpected for a macroblock.

The encoder may initialize 440 to zero a counter associated with thenumber of bits in a current entropy slice. The counter value may bedenoted A for illustrative purposes in the remainder of the descriptionof the embodiments of the present invention described in relation toFIG. 16. The syntax elements for a next macroblock may be obtained 442.The next macroblock may be determined according to a predefinedmacroblock processing order. In some embodiments, the macroblockprocessing order may correspond to a raster-scan ordering. Non-binarysyntax elements in the macroblock may be converted 444 to a string ofbins. Binary syntax elements may not require conversion. The binsassociated with the macroblock may be entropy encoded 446, and thenumber of bins associated with the macroblock may be determined 448. Thenumber of accumulated bits associated with the current entropy slice maybe updated 450 to include the bins associated with the macroblock, andthe entropy encoded bins associated with the macroblock may be written452 to the bitstream. The number of accumulated bins associated with thecurrent entropy slice is compared 454 with a threshold. If the number ofaccumulated bits associated with the current entropy slice is greaterthan the threshold based on the maximum number of bits allowed in anentropy slice 456, then the encoder may start 458 a new entropy slice,and initialize 460 to zero the counter associated with the number ofbits in a current entropy slice. The syntax elements for the nextmacroblock may be obtained 442, and the partitioning process maycontinue. If the number of accumulated bits associated with the currententropy slice is not greater than a threshold based on the maximumnumber of bits allowed in an entropy slice 455, then the syntax elementsfor the next macroblock may be obtained 442, and the partitioningprocess may continue.

In alternative embodiments of the present invention, an encoder maypartition a reconstruction slice into a plurality of entropy slices,wherein each entropy slice may be associated with no more than apredefined number of macroblocks.

In some embodiments of the present invention, a restriction on themaximum number of macroblocks in a reconstruction slice may be imposedin addition to a restriction on the size of an entropy slice.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices, wherein thesize of each entropy slice may be restricted to less than a predefinednumber of macroblocks and to less than a predefined number of bins.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices, wherein thesize of each entropy slice may be restricted to less than a predefinednumber of macroblocks and to less than a predefined number of bits.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices, wherein thesize of each entropy slice may be restricted to less than a predefinednumber of macroblocks, to less than a predefined number of bins and toless than a predefined number of bits.

In some embodiments of the present invention, bin coding within anentropy coder may be parallelized allowing parallel encoding of morethan one bin, which may reduce encoding time. These embodiments of thepresent invention may be understood in relation to an exemplary entropycoder depicted in FIG. 17. In these embodiments, the entropy coder 480may comprise a context-adaptation unit 482, a state-based, bin-coderselector 484 and a plurality of bin coders, also considered bin-coderunits, (three shown) 486, 488, 500 that may operate in parallel. Bins502 may be made available to the entropy coder 480 from a binarizer 504that may generate the bins 502 from input symbols 506. The bins 502 maybe made available to the context-adaptation unit 482 and thestate-based, bin-coder selector 484. The context-adaptation unit 482 mayperform context adaptation and generate a model state, also referred toas a state, 508 that may be used to select the bin coder 486, 488, 500to which a bin 502 may be directed. The state-based, bin-coder selector484 may select the bin coder 486, 488, 500 associated with the generatedmodel state 508 to encode the bin. In some embodiments (not shown), thegenerated state 508 may be made available to the selected bin coder.Output bits 510, 512, 514 may be generated by the bin coders 486, 488,500, and the output bits 510, 512, 514 may be incorporated into abitstream. In some embodiments of the present invention, the output bits510, 512, 514 may be buffered and incorporated into the bitstream byconcatenation. In alternative embodiments, the output bits 510, 512, 514may be buffered and incorporated into the bitstream according to aninterleaving scheme.

According to embodiments of the present invention described in relationto FIG. 17, a first bin may be sent to a first bin coder in response toa first model state generated in relation to the first bin. Thecontext-adaptation unit 482, upon completion of processing the firstbin, may begin processing of a second bin, sending the second bin to asecond bin coder in response to a second model state generated inrelation to the second bin, thereby allowing substantially parallelprocessing of more than one bin.

In alternative embodiments of the present invention, an entropy codermay comprise a plurality of context-adaptation units that may operate inparallel and a single bin coder. In systems wherein thecontext-adaptation units require longer processing time than the bincoder, a plurality of context-adaptation units operating in parallel mayreduce encoding time. Some of these embodiments of the present inventionmay be understood in relation to an exemplary entropy coder depicted inFIG. 18. In these embodiments, the entropy coder 530 may comprise aplurality of context-adaptation units (three shown) 532, 534, 536, acontext-adaptation-unit selector 538, a state selector 540 and a bincoder 542. Bins 544 may be made available to the entropy coder 530 froma binarizer 546 that may generate the bins 544 from input symbols 548.The bins 544 may be made available to the context-adaptation-unitselector 538, the state selector 540 and the bin coder 542. Thecontext-adaptation-unit selector 538 may be used to select, or toschedule, a context-adaptation unit 532, 534, 536 to which a bin 544 maybe directed and from which a state value 550, 552, 554 may be generated.In some exemplary embodiments, the context-adaptation-unit selector 538may select a context-adaptation unit 532, 534, 536 based on the syntaxassociated with the bin, for example a context-adaptation unitidentifier may be associated with a bin identifying thecontext-adaptation unit to which the bin may be directed for processing.In alternative exemplary embodiments, the context-adaptation-unitselector 538 may select a context-adaptation unit 532, 534, 536 based ona scheduling protocol or load-balancing constraint associated with thecontext-adaptation units 532, 534, 536. In some embodiments, thegenerated state value may be selected by the state selector 540,according to the criterion used at the context-adaptation unit selector538, at the appropriate timing to be passed to the bin coder 542. Thebin coder 542 may use the state value 556 passed by the state selector540 in coding the bin 544. In alternative embodiments of the presentinvention (not shown), the state value may not be required by the bincoder and, therefore, not made available to the bin coder. Output bits558 may be generated by the bin coder 542, and the output bits 558 maybe incorporated into a bitstream. In some embodiments of the presentinvention, the output bits 558 may be buffered and incorporated into thebitstream by concatenation. In alternative embodiments, the output bits558 may be buffered and incorporated into the bitstream according to aninterleaving scheme.

In yet alternative embodiments of the present invention, an entropycoder may comprise a plurality of context-adaptation units that mayoperate in parallel and a plurality of bin coders that may operate inparallel. These embodiments of the present invention may be understoodin relation to an exemplary entropy coder depicted in FIG. 19. In theseembodiments, the entropy coder 570 may comprise a plurality ofcontext-adaptation units (three shown) 572, 574, 576, acontext-adaptation-unit selector 578, a state selector 580, astate-based, bin-coder selector 582 and a plurality of bin coders (threeshown) 584, 586, 588. Bins 590 may be made available to the entropycoder 570 from a binarizer 592 that may generate the bins 590 from inputsymbols 594. The bins 590 may be made available to thecontext-adaptation-unit selector 578, the state selector 580 and thebin-coder selector 582. The context-adaptation-unit selector 578 may beused to select, or to schedule, a context-adaptation unit 572, 574, 576to which a bin 590 may be directed and from which a state value 596,598, 600 may be generated. The generated state value may be selected bythe state selector 580 at the appropriate timing to be passed to thestate-based, bin-coder selector 582. The state-based, bin-coder selector582 may use the state value 602 passed by the state selector 580 toselect the bin coder 584, 586, 588 to which a bin 590 may be directed.In alternative embodiments (not shown), the state value 602 may be madeavailable to the selected bin coder. The selected bin coder may use thestate value 602 in coding the bin 590. In alternative embodiments of thepresent invention (not shown), the state value may not be required bythe bin coder and, therefore, not made available to the bin coder.Output bits 604, 606, 608 may be generated by the bin coders 584, 586,588 and the output bits 604, 606, 608 may be incorporated into abitstream. In some embodiments of the present invention, the output bits604, 606, 608 may be buffered and incorporated into the bitstream byconcatenation. In alternative embodiments, the output bits 604, 606, 608may be buffered and incorporated into the bitstream according to aninterleaving scheme

An exemplary embodiment of the present invention may comprise aplurality of variable length coding codecs that may operate in parallel.

In one exemplary embodiment of the present invention, a bin coder maycomprise binary arithmetic coding. In another exemplary embodiment ofthe present invention, a bin coder may comprise variable length coding.In yet another exemplary embodiment of the present invention, a bincoder may comprise fixed length coding.

In general, an entropy coder may comprise N_(ca) context-adaptationunits and N_(bc), bin-coder units, where N_(ca) is an integer greaterthan, or equal to, one and N_(bc) is an integer greater than, or equalto, one.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices, wherein thesize of each entropy slice may be restricted such that one, or more, ofN_(ca) context-adaptation units and N_(bc) bin-coder units may eachoperate on no more than a limited number of bins during the processingof the entropy slice. Context-adaptation units and bin-coder units withsuch a restriction may be referred to as restricted entropy-coder units.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices, wherein thesize of each entropy slice may be restricted such that none of theN_(ca) context-adaptation units may operate on more than B_(ca) binsduring the processing of an entropy slice. In some embodiments of thepresent invention, the value of B_(ca) may be signaled, for example, ina bitstream, profile constraint, level constraint or other normativemechanism.

In alternative embodiments of the present invention, an encoder maypartition a reconstruction slice into a plurality of entropy slices,wherein the size of each entropy slice may be restricted such that noneof the N_(bc) bin-coder units may operate on more than B_(bc) binsduring the processing of an entropy slice. In some embodiments of thepresent invention, the value of B_(bc) may be signaled, for example, ina bitstream, profile constraint, level constraint or other normativemechanism.

In yet alternative embodiments of the present invention, an encoder maypartition a reconstruction slice into a plurality of entropy slices,wherein the size of each entropy slice may be restricted such that noneof the N_(ca) context-adaptation units may operate on more than B_(ca)bins and none of the N_(bc) bin-coder units may operate on more thanB_(bc) bins during the processing of an entropy slice. In someembodiments of the present invention, the value of B_(bc) and the valueof B_(ca) may be signaled, for example, in a bitstream, profileconstraint, level constraint or other normative mechanism.

In still alternative embodiments of the present invention, an encodermay partition a reconstruction slice into a plurality of entropy slices,wherein the size of each entropy slice may be restricted such that theith N_(ca) context-adaptation unit, denoted N_(ca)(i), for i=1, . . . ,N_(ca), may operate on no more than B_(ca)(i) bins and the ith N_(bc)bin-coder unit, N_(bc)(i), for i=1, . . . , N_(bc), may operate on nomore than B_(bc)(i) bins during the processing of an entropy slice. Insome embodiments of the present invention, the values of the B_(bc)(i)and the values of the B_(ca)(i) may be signaled, for example, in abitstream, profile constraint, level constraint or other normativemechanism.

Some exemplary embodiments of the present invention may be described inrelation to FIG. 20. In these embodiments, an encoder may, for areconstruction slice, partition the reconstruction slice into aplurality of entropy slices, wherein the size of each entropy slice maybe restricted such that one, or more, of N_(ca) context-adaptation unitsand N_(bc) bin-coder units may operate on no more than a limited numberof bins. The encoder may initialize 650 to zero a counter, for eachrestricted entropy-coder unit, associated with the number of binsprocessed in a current entropy slice. For illustrative purposes in theremainder of the description of the embodiments of the present inventiondescribed in relation to FIG. 20, the counter value may be denoted A,where A represents a vector with each entry in the vector correspondingto the accumulated number of processed bins, for the current entropyslice, by a restricted entropy-coder unit. The syntax elements for anext macroblock may be obtained 652. The next macroblock may bedetermined according to a predefined macroblock processing order. Insome embodiments, the macroblock processing order may correspond to araster-scan ordering. Non-binary syntax elements in the macroblock maybe converted 654 to a string of bins. Binary syntax elements may notrequire conversion. The number of bins, associated with the macroblock,processed by each restricted entropy-coder unit may be determined 656.The number of bins associated with the macroblock may include the binsin the strings of bins associated with the non-binary syntax elements inaddition to the binary syntax elements. For illustrative purposes in theremainder of the description of the embodiments of the present inventiondescribed in relation to FIG. 20, the number of bins, associated withthe macroblock, processed by each restricted entropy-coder unit may bedenoted num, where num represents a vector with each entry in the vectorcorresponding to the number of processed bins, for the currentmacroblock, by a restricted entropy-coder unit.

If the number of bins associated with the macroblock for each restrictedentropy-coder unit may be added 658 to the number of already accumulatedbins, associated with the current entropy slice, for each restrictedentropy-coder unit, without 659 exceeding a maximum number of binsallowed for any restricted entropy-coder unit, then the number ofaccumulated bins associated with the current entropy slice may beupdated 660 to include the bins associated with the macroblock, and thebins associated with the macroblock may be written 662, by the entropyencoder, to the bitstream and associated with the current entropy slice.The syntax elements for the next macroblock may be obtained 652, and thepartitioning process may continue.

If the sum 658 of the number of bins associated with the macroblock andthe number of already accumulated bins associated with the currententropy slice exceeds 663 the maximum number of bins allowed for anyrestricted entropy-coder unit, then the encoder may start 664 a newentropy slice associated with the current reconstruction slice, and thecounter associated with the number of bins in the current entropy slicemay be initialized 666 to zero. The number of accumulated binsassociated with the current entropy slice may be updated 660 to includethe bins associated with the macroblock, and the bins associated withthe macroblock may be written 662, by the entropy encoder, to thebitstream and associated with the current entropy slice. The syntaxelements for the next macroblock may be obtained 652, and thepartitioning process may continue.

Some embodiments of the present invention may be described in relationto FIG. 21. In these embodiments, an encoder may, for a reconstructionslice, partition the reconstruction slice into a plurality of entropyslices, wherein the size of each entropy slice may be restricted suchthat one, or more, of N_(ca) context-adaptation units and N_(bc)bin-coder units may operate on no more than a limited number of bins.The encoder may initialize 700 to zero a counter, for each restrictedentropy-coder unit, associated with the number of bins processed in acurrent entropy slice by the restricted entropy-coder unit. Forillustrative purposes in the remainder of the description of theembodiments of the present invention described in relation to FIG. 21,the counter value may be denoted A, where A represents a vector witheach entry in the vector corresponding to the accumulated number ofprocessed bins, for the current entropy slice, by a restrictedentropy-coder unit. In these embodiments, the encoder may associatemacroblock syntax elements with an entropy slice until the number ofbins processed by a restricted entropy-coder unit reaches a thresholdassociated with the predetermined maximum number of bins allowed to beprocessed, in an entropy slice, by the restricted entropy-coder unit. Insome embodiments, the threshold may be a percentage of the maximumnumber of bins allowed to be processed, in an entropy slice, by therestricted entropy-coder unit. In one exemplary embodiment, thethreshold may be 90% of the maximum number of bins allowed to beprocessed, in an entropy slice, by the restricted entropy-coder unit,supposing that the greatest number of bins expected in a macroblock tobe processed by the restricted entropy-coder unit is less than 10% ofthe maximum number of bins allowed to be processed, in an entropy slice,by the restricted entropy-coder unit. In another exemplary embodiment,the threshold may be a percentage of the maximum number of bins allowedto be processed, in an entropy slice, by a restricted entropy-coder unitwherein the percentage may be based on the greatest number of binsexpected in a macroblock to be processed by the restricted entropy-coderunit. In these embodiments, once the size of an entropy slice exceeds athreshold size, then another entropy slice may be created. The thresholdsize may be selected to ensure that the entropy slice does not exceedthe maximum number of bins allowed to be processed by any one restrictedentropy-coder unit in an entropy slice. In some embodiments, thethreshold size may be a function of the maximum number of bins allowedin an entropy slice and an estimate of the maximum number of binsexpected for a macroblock.

The syntax elements for a next macroblock may be obtained 702. The nextmacroblock may be determined according to a predefined macroblockprocessing order. In some embodiments, the macroblock processing ordermay correspond to a raster-scan ordering. Non-binary syntax elements inthe macroblock may be converted 704 to a string of bins. Binary syntaxelements may not require conversion. The bins associated with themacroblock may be written 706, by the entropy encoder, to the bitstreamand associated with the current entropy slice. The number of bins,associated with the macroblock, processed by each restrictedentropy-coder unit may be determined 708. The number of bins associatedwith the macroblock may include the bins in the strings of binsassociated with the non-binary syntax elements in addition to the binarysyntax elements. For illustrative purposes in the remainder of thedescription of the embodiments of the present invention described inrelation to FIG. 21, the number of bins, associated with the macroblock,processed by each restricted entropy-coder unit may be denoted num,where num represents a vector with each entry in the vectorcorresponding to the number of processed bins, for the currentmacroblock, by a corresponding restricted entropy-coder unit. The numberof accumulated bins, associated with the current entropy slice,processed by each restricted entropy-coder unit may be updated 710 toinclude the bins associated with the macroblock. The number ofaccumulated bins associated with the current entropy slice is compared712 with a threshold. If the number of accumulated bins associated withthe current entropy slice, processed by a restricted entropy-coder unitis greater than the threshold, which may be denoted TH(MaxNumBins)(i)for restricted entropy-coder unit i, 714, then the encoder may start 716a new entropy slice, and initialize 718 to zero the counter associatedwith the number of bins processed by each restricted entropy-coder unitin a current entropy slice. The syntax elements for the next macroblockmay be obtained 702, and the partitioning process may continue. If thenumber of accumulated bins, associated with the current entropy slice,processed by a restricted entropy-coder unit is not greater than thethreshold 713, then the syntax elements for the next macroblock may beobtained 702, and the partitioning process may continue.

Some embodiments of the present invention may comprise a combination ofthe above-described criteria for entropy slice partitioning.

It is to be understood that while some embodiments of the presentinvention may restrict the size of an entropy slice to be less than afirst predefined size, that the size of the entropy slice may beequivalently restricted to not exceed a second predefined size. Theembodiments described herein are exemplary embodiments of the presentinvention, and a person of ordinary skill in the art will appreciatethat there are equivalent embodiments of the present invention forrestricting the size of an entropy slice.

In some embodiments of the present invention, starting a new entropyslice may comprise terminating the current slice and considering the newentropy slice the current entropy slice.

In some embodiments of the present invention, the decoding of aplurality of bits within an entropy slice may be parallelized within anentropy decoder comprising a plurality of bin decoders, which may reducedecoding time. Exemplary embodiments of the present invention may beunderstood in relation to an exemplary entropy decoder 750, depicted inFIG. 22, comprising a plurality (three shown) of bin decoders 762, 764,766. Bits 752 within an entropy slice and previously decoded symbols 754may be made available to an entropy decoder 750. The bits 752 may bemade available to a bin-decoder selector 756 which may select, based ona context state 758 generated from a context-adaptation unit 760, a bindecoder 762, 764, 766. The context-adaptation unit 760 may generate thecontext state 758 based on the previously decoded symbols 754 madeavailable to the context-adaptation unit 760. The bin-decoder selector756 may assign a bin-decoder 762, 764, 766 based on the context state756. The bit to be decoded 752 may be passed by the bin-decoder selector756 to the selected bin decoder. The bin decoders 762, 764, 766 maygenerate decoded bins 768, 770, 772 which may be multiplexed by amultiplexer 774 and the multiplexed bins 776 may be sent to a symbolizer778 which may generate the symbols 754 associated with the bins 776.

In some embodiments of the present invention, decoding of a plurality ofbits within an entropy slice may be parallelized within an entropydecoder comprising a plurality of context-adaptation units, which mayreduce decoding time. Exemplary embodiments of the present invention maybe understood in relation to an exemplary entropy decoder 800, depictedin FIG. 23, comprising a plurality (three shown) of context-adaptationunits 814, 816, 818. Bits 802 within an entropy slice and previouslydecoded symbols 810 may be made available to an entropy decoder 800. Thebits 802 may be made available to a context-adaptation unit selector 812that may select from a plurality of context-adaptation units 814, 816,818 a context-adaptation unit for the decoding process of an input bit.In some embodiments of the present invention, the context-adaptationunit selector 812 may select the Nth context-adaptation unit whenreceiving every Nth bit. The selected context-adaptation unit maygenerate a context state 820, 822, 824 based on the previously decodedsymbols 810 made available to the selected context-adaptation unit. Astate selector 826, at the appropriate timing, may select the generatedcontext state in associated with an input bit. In some embodiments ofthe present invention, state selector 826 may select the Nthcontext-adaptation unit when receiving every Nth bit according to thesame procedure as the context-adaptation unit selector 812. The selectedstate 828 may be made available to the bin decoder 804. The bin decoder804 may decode the bit 802 and send the decoded bin to a symbolizer 808which may generate a symbol 810 associated with the decoded bin 806.

In some embodiments of the present invention, decoding of a plurality ofbits within an entropy slice may be parallelized within an entropydecoder comprising a plurality of context-adaptation units and aplurality of bin decoders, which may reduce decoding time. Exemplaryembodiments of the present invention may be understood in relation to anexemplary entropy decoder 850, depicted in FIG. 24, comprising aplurality (three shown) of context-adaptation units 852, 854, 856 and aplurality (three shown) of bin decoders 858, 860, 862. Bits 864 withinan entropy slice and previously decoded symbols 866 may be madeavailable to an entropy decoder 850. The bits 864 may be made availableto a context-adaptation unit selector 868 that may select from theplurality of context-adaptation units 852, 854, 856 a context-adaptationunit for the decoding process of an input bit. In some embodiments ofthe present invention, the context-adaptation unit selector 868 mayselect the Nth context-adaptation unit when receiving every Nth bit. Theselected context-adaptation unit may generate a context state 870, 872,874 based on the previously decoded symbols 866 made available to theselected context-adaptation unit. A state selector 876, at theappropriate timing, may select the generated context state in associatedwith an input bit. In some embodiments of the present invention, stateselector 876 may select the Nth context-adaptation unit when receivingevery Nth bit according to the same procedure as the context-adaptationunit selector 868. The selected state 878 may be made available to abin-decoder selector 880, which may select, based on the selectedcontext state 878, a bin decoder 858, 860, 862. The bin-decoder selector880 may assign a bin-decoder 858, 860, 862 based on the context state878. The bit to be decoded 864 may be passed by the bin-decoder selector880 to the selected bin decoder. The bin decoders 858, 860, 862 maygenerate decoded bins 882, 884, 886 which may be multiplexed by amultiplexer 888 and the multiplexed bins 890 may be sent to a symbolizer892 which may generate the symbols 866 associated with the bins 864.

In some embodiments of the present invention, an encoder may partition areconstruction slice into a plurality of entropy slices, wherein themacroblocks within an entropy slice are contiguous. FIG. 25 depicts anexemplary reconstruction slice 950 partitioned into three entropyslices: entropy slice 0 shown in cross-hatch 952, entropy slice 1 shownin white 954 and entropy slice 2 shown in dot-hatch 956. The macroblockswithin each entropy slice 952, 954, 956, in this exemplaryreconstruction slice 950, are contiguous.

In alternative embodiments of the present invention, an encoder maypartition a reconstruction slice into a plurality of entropy slices,wherein the macroblocks within an entropy slice may not be contiguous.FIG. 26 depicts an exemplary reconstruction slice 960 partitioned intothree entropy slices: entropy slice 0 shown in cross-hatch 962, entropyslice 1 shown in white 964 and entropy slice 2 shown in dot-hatch 966.The macroblocks within each entropy slice 962, 964, 966, in thisexemplary reconstruction slice 960, are not contiguous. A partition of areconstruction slice in which the macroblocks within an entropy sliceare not contiguous may be referred to as an interleaved partition.

In some embodiments of the present invention, during the entropydecoding of a current block within an entropy slice, the decoder may useother blocks from the same entropy slice to predict information relatedto the entropy decoding of the current block. In some embodiments of thepresent invention, during reconstruction of a current block within areconstruction slice, other blocks from the same reconstruction slicemay be used to predict information related to the reconstruction of thecurrent block.

In some embodiments of the present invention in which a reconstructionslice comprises an interleaved partition, neighboring blocks within anentropy slice used in the decoding of a current block within the entropyslice may not be directly neighboring, or contiguous. FIG. 27illustrates this situation for the exemplary interleaved partitiondepicted in FIG. 26.

In FIG. 27, for a current macroblock 970 within an entropy slice 964,the left-neighbor block used for entropy decoding of the currentmacroblock 970 is the contiguous, left-neighbor block 972 within theentropy slice 964. The upper-neighbor block used for entropy decoding ofthe current macroblock 970 is the non-contiguous, upper-neighbor block974 within the same entropy slice 964. For reconstruction of the currentmacroblock 970, the left-neighbor block is the contiguous, left-neighborblock 972 within the reconstruction slice 960, and the upper-neighborblock is the contiguous, upper-neighbor block 976 within thereconstruction slice 960.

In some embodiments of the present invention in which a reconstructionslice comprises an interleaved partition, there may be no appropriateneighboring block within an entropy slice to be used in the decoding ofa current block within the entropy slice. FIG. 28 illustrates thissituation for the exemplary interleaved partition depicted in FIG. 26.

In FIG. 28, for a current block 980 within an entropy slice 964, thereis no left-neighbor block within the entropy slice 964 to be used forentropy decoding of the current block 980. The upper-neighbor block usedfor entropy decoding of the current block 980 is the non-contiguous,upper-neighbor block 982 within the same entropy slice 964. Forreconstruction of the current block 980, the left-neighbor block is thecontiguous, left-neighbor block 984 within the reconstruction slice 960,and the upper-neighbor block is the contiguous, upper-neighbor block 986within the reconstruction slice 960.

In some embodiments of the present invention, a decoder may pre-processa complete incoming bitstream to identify the locations of the entropyslices. In some embodiments of the present invention, a decoder maypre-process an entire reconstruction slice to identify the locations ofthe entropy slices within the reconstruction slice. In some embodiments,the locations of the entropy slices may be determined by identifying thelocations of the entropy-slice headers. In these embodiments, thedecoder may read the bits in the bitstream and pre-defined start-codevalues may be identified.

In alternative embodiments, entropy-slice headers may be constrained toa range of bits located at pre-defined positions within an incomingbitstream. In alternative embodiments, entropy-slice headers may beconstrained to a range of bytes located at pre-defined positions withinan incoming bitstream. In these embodiments, either bit aligned or bytealigned, a decoder need not pre-process significantly large portions ofthe incoming bitstream to locate the entropy slices.

In some embodiments of the present invention, an encoder may signal, inthe bitstream, entropy-slice-location information, also referred to asentropy-slice-location parameters, for example, offset and rangeinformation, that may constrain the locations of the entropy-sliceheaders. In alternative embodiments, entropy-slice-location informationmay not be signaled in the bitstream, but may be determined fromentropy-slice parameters, for example, a fixed number of bins allowed inany given entropy slice, a fixed number of bits allowed in any givenentropy slice and other entropy-slice parameters. In still alternativeembodiments of the present invention, entropy-slice-location informationmay be defined by other normative means, for example, the informationmay be specified in a profile constraint, a level constraint, anapplication constraint, or other constraint, or the information may besignaled as supplemental information or signaled by other out-of-boundmeans.

In some embodiments of the present invention, one set ofentropy-slice-location parameter values may be used for all entropyslices within a bitstream. In alternative embodiments,entropy-slice-location parameter values may be defined for a group ofpixels represented by a portion of a sequence. In alternativeembodiments, entropy-slice-location parameter values may be defined foreach picture within a bitstream and may be used for all entropy sliceswithin the associated picture. In alternative embodiments,entropy-slice-location parameter values may be defined for eachreconstruction slice within a bitstream and may be used for all entropyslices within the associated reconstruction slice. In yet alternativeembodiments, multiple sets of entropy-slice-location parameter valuesmay be used by the decoder. In still alternative embodiments,entropy-slice-location parameter values may be assigned to entropy-sliceidentifiers, for example, a first entropy-slice header may use a firstset of entropy-slice-location parameter values, a second entropy-sliceheader may use a second set of entropy-slice-location parameter valuesand, in general, an Nth entropy-slice header may use an Nth set ofentropy-slice-location parameter values. In some embodiments of thepresent invention, entropy-slice-parameter values may be assigned toframe identifiers. In one exemplary embodiment, a first picture may usea first set of entropy-slice-parameter values, a second picture may usea second set of entropy-slice-parameter values and, in general, an Nthpicture may use an Nth set of entropy-slice-location parameter values.In another exemplary embodiment, a picture of a first type may use afirst set of entropy-slice-location parameter values and a picture of asecond type may use a second set of entropy-slice-location parametervalues. Exemplary types of pictures are intra pictures, predictedpictures and other types of pictures.

In some embodiments of the present invention comprising an H.264/AVCcodec, an entropy-slice offset and an entropy-slice range may besignaled in a sequence parameter set Raw Byte Sequence Payload (RBSP) byadding an “entropy_slice_offset” parameter and an “entropy_slice_range”to the sequence parameter set. Table 3 lists exemplary sequenceparameter set RBSP syntax according to embodiments of the presentinvention.

In some embodiments of the present invention comprising an H.264/AVCcodec, an entropy-slice offset and an entropy-slice range may besignaled in a picture parameter set Raw Byte Sequence Payload (RBSP) byadding an “entropy_slice_offset” parameter and an “entropy_slice_range”to the picture parameter set. Table 4 lists exemplary picture parameterset RBSP syntax according to embodiments of the present invention.

In some embodiments of the present invention comprising an H.264/AVCcodec, an entropy-slice offset and an entropy-slice range may besignaled in a slice header by adding an “entropy_slice_offset” parameterand an “entropy_slice_range” to the slice header. Table 5 listsexemplary slice header syntax according to embodiments of the presentinvention.

In some embodiments of the present invention, an entropy-slice offsetand an entropy-slice range may be indicated for each level conformancepoint of the encoder according to a table, for example, as shown inTable 6, where O_(m.n) denotes the entropy-slice offset for a level m.nconformance point and R_(m.n) denotes the entropy-slice range for a m.nconformance point.

TABLE 3 Exemplary Sequence Parameter Set RBSP Syntax Table C Descriptorseq_parameter_set_rbsp( ) {  profile_idc 0 u(8)  reserved_zero_8bits /*equal to 0 */ 0 u(8)  level_idc 0 u(8)  seq_parameter_set_id 0 ue(v) bit_depth_luma_minus8 0 ue(v)  bit_depth_chroma_minus8 0 ue(v) increased_bit_depth_luma 0 ue(v)  increased_bit_depth_chroma 0 ue(v) log2_max_frame_num_minus4 0 ue(v)  log2_max_pic_order_cnt_lsb_minus4 0ue(v)  max_num_ref_frames 0 ue(v)  gaps_in_frame_num_value_allowed_flag0 u(1)  log2_min_coding_unit_size_minus3 0 ue(v) max_coding_unit_hierarchy_depth 0 ue(v) log2_min_transform_unit_size_minus2 0 ue(v) max_transform_unit_hierarchy_depth 0 ue(v)  pic_width_in_luma_samples 0u(16)  pic_height_in_luma_samples 0 u(16)  entropy_slice_offset 0 ue(v) entropy_slice_range 0 ue(v)  rbsp_trailing_bits( ) 0 }

TABLE 4 Exemplary Picture Parameter Set RBSP Syntax Table C Descriptorpic_parameter_set_rbsp( ) {  pic_parameter_set_id 1 ue(v) seq_parameter_set_id 1 ue(v)  entropy_coding_mode_flag 1 u(1) num_ref_idx_l0_default_active_minus1 1 ue(v) num_ref_idx_l1_default_active_minus1 1 ue(v)  pic_init_qp_minus26 /*relative to 26 */ 1 se(v)  constrained_intra_pred_flag 1 u(1) entropy_slice_offset 0 ue(v)  entropy_slice_range 0 ue(v) rbsp_trailing_bits( ) 1 }

TABLE 5 Exemplary Syntax Table for Slice Header C Descriptor sliceheader( ) {   first_lctb_in_slice 2 ue(v)   slice_type 2 ue(v)  pic_parameter_set_id 2 ue(v)   frame_num 2 u(v)   if( IdrPicFlag )   idr_pic_id 2 ue(v)   pic_order_cnt_lsb 2 u(v)   if( slice_type == P || slice_type == B ) {    num_ref_idx_active_override_flag 2 u(1)    if(num_ref_idx_active_override_flag ) {     num_ref _idx_l0_active_minus1 2ue(v)     if( slice_type == B )      num_ref_ idx_l1_active_minus1 2ue(v)    }   }   if( nal_ref_ idc !=0 )    dec_ref_pic_marking( ) 2  if( entropy_coding_mode_flag && slice_type !=I )    cabac_init_idc 2ue(v)   slice_qp_delta 2 se(v)   alf_param( )   if( slice_type == P | |slice_type == B) {   mc_interpolation_idc 2 ue(v)   mv_competition_flag2 u(1)    if ( mv_competition_flag ) {     mv_competition_temporal_flag2 u(1)    }  }   if ( slice_type == B && mv_competition_flag)  collocated_from_l0_flag 2 u(1)   entropy_slice_offset 0 ue(v)  entropy_slice_range 0 ue(v) }

TABLE 6 Exemplary Entropy-Slice Offset and Entropy-Slice Range for EachLevel Level Entropy Slice Offset Entropy Slice Range 1.1 O_(1.1) R_(1.1)1.2 O_(1.2) R_(1.2) . . . . . . . . . m.n O_(m.n) R_(m.n) . . . . . . .. . 5.1 O_(5.1) R_(5.1)

In some embodiments, entropy-slice-location information may compriseinformation that may constrain the locations of the entropy-sliceheaders. In one example, entropy-slice-location information may comprisean offset, also referred to as a period or base offset, value and arange, also referred to as a deviation or offset for a period, value. Anentropy-slice-header location may be constrained based on the offsetvalue and the range value. In some embodiments of the present invention,an offset value and a range value may be defined explicitly. Inalternative embodiments of the present invention, an offset value and arange value may be implicitly defined as a minimum offset value and amaximum offset value. In still alternative embodiments of the presentinvention, an offset value and a range value may be implicitly definedas a maximum offset value and the difference between the maximum offsetvalue and a minimum offset value. In yet alternative embodiments of thepresent invention, an offset value and a range value may be implicitlydefined as a minimum offset value and the difference between the minimumoffset value and a maximum offset value. In alternative embodiments, anoffset value and a range value may be implicitly defined as a thirdvalue and the difference between the third value and a maximum offsetvalue and a minimum offset value. In still alternative embodiments, anoffset value and a range value may be defined through an index into alook-up table that contains the corresponding minimum and maximumbit-values. In some embodiments, an offset value and a range value maybe defined using an offset based look-up tree. In some embodiments, anoffset value and a range value may be defined using cost-minimizingindexing. A person having ordinary skill in the art will recognize thatthere are many methods known in the art for implicitly defining a rangevalue and an offset value and for assuring that an encoder and a decoderoperate with the same value for the pre-defined offset and range values.

In some embodiments of the present invention, signaling a range valuemay be optional. In some embodiments, when a range value is notsignaled, then the range value may be set to a pre-defined value. In anexemplary embodiment, the pre-defined value may be zero. In anotherexemplary embodiment, the pre-defined value may be a non-zero integervalue.

In an exemplary embodiment described in relation to FIG. 29, theentropy-slice header associated with an entropy slice, slice number Nwithin a reconstruction slice, may be constrained to start after Nk−pbits from the start of, or other fixed location within, thereconstruction-slice header, where k denotes the offset value and pdenotes the range. The location from which the Nk−p bits may be measuredmay be referred to as the reference location. In alternativeembodiments, a reference location may not be associated with aparticular reconstruction slice and may be the same fixed locationwithin a bitstream for all entropy slices. In alternative embodiments,the entropy-slice header may be byte aligned, and the constraint may beassociated with a number of bytes. While the example illustrated inrelation to FIG. 29 is described in terms of bits, a person havingordinary skill in the art may appreciate the alternative byte-alignedembodiments.

FIG. 29 is a pictorial representation of an exemplary portion 1000 of anexemplary bitstream. The bitstream portion 1000 comprises areconstruction-slice header 1002, represented by a solid blackrectangle, four entropy-slice headers (the entropy-slice headercorresponding to the zeroth entropy slice 1003, referred to as thezeroth entropy-slice header, the entropy-slice header corresponding tothe first entropy slice 1004, referred to as the first entropy-sliceheader, the entropy-slice header corresponding to the second entropyslice 1005, referred to as the second entropy-slice header, theentropy-slice header corresponding to the third entropy slice 1006,referred to as the third entropy-slice header), represented by solidgray rectangles, and remaining portions of the entropy slices,represented by thin, black-and-white stripes. In this example, thereference location may be the start 1001 of the reconstruction-sliceheader 1002. In some embodiments of the present invention, theentropy-slice header corresponding to the zeroth entropy slice 1003 maybe constrained to be located immediately after the reconstruction-sliceheader 1002. In some embodiments of the present invention, theentropy-slice header corresponding to the zeroth entropy slice may be apart of the reconstruction-slice header. In these embodiments, thereconstruction-slice header may comprise a reconstruction portion and anentropy portion. In some embodiments of the present invention depictedin FIG. 29, the first entropy-slice header 1004 may be constrained to belocated after k−p bits 1007 from the reference location 1001, the secondentropy-slice header 1005 may be constrained to be located after 2k−pbits 1008 from the reference location 1001, the second entropy-sliceheader 1006 may be constrained to be located after 3k−p bits 1009 fromthe reference location 1001. In these embodiments, an entropy decoderassigned to decode entropy slice N may begin searching for thecorresponding entropy-slice header after Nk−p bits from the referencelocation 1001.

In alternative embodiments of the present invention, theentropy-slice-location information may not comprise a range parameter.In these embodiments, an entropy decoder may begin searching for the Nthentropy-slice header after Nk bits from a reference location.

In another exemplary embodiment described in relation to FIG. 30, theentropy-slice header associated with entropy slice, slice number Nwithin a reconstruction slice, may be constrained to start after Nk−pbits from the start of, or other fixed location within, thereconstruction-slice header, where k denotes the offset value and pdenotes the range, and the entropy-slice header may further beconstrained to be within a 2p range of bits from the constrainedstarting location. The location from which the Nk−p bits may be measuredmay be referred to as the reference location. In alternativeembodiments, a reference location may not be associated with aparticular reconstruction slice and may be the same fixed locationwithin a bitstream for all entropy slices. In alternative embodiments,the entropy-slice header may be byte aligned, and the constraint may beassociated with a number of bytes. While the example illustrated inrelation to FIG. 30 is described in terms of bits, a person havingordinary skill in the art may appreciate the alternative byte-alignedembodiments.

FIG. 30 is a pictorial representation of an exemplary portion 1020 of anexemplary bitstream. The bitstream portion 1020 comprises areconstruction-slice header 1022, represented by a solid blackrectangle, four entropy-slice headers (the entropy-slice headercorresponding to the zeroth entropy slice 1023, referred to as thezeroth entropy-slice header, the entropy-slice header corresponding tothe first entropy slice 1024, referred to as the first entropy-sliceheader, the entropy-slice header corresponding to the second entropyslice 1025, referred to as the second entropy-slice header, theentropy-slice header corresponding to the third entropy slice 1026,referred to as the third entropy-slice header), represented by solidgray rectangles, and remaining portions of the entropy slices,represented by thin, black-and-white stripes. In this example, thereference location may be the start 1021 of the reconstruction-sliceheader 1022. In some embodiments of the present invention, theentropy-slice header corresponding to the zeroth entropy slice 1023 maybe constrained to be located immediately after the reconstruction-sliceheader 1022. In some embodiments of the present invention, theentropy-slice header corresponding to the zeroth entropy slice may be apart of the reconstruction-slice header. In these embodiments, thereconstruction-slice header may comprise a reconstruction portion and anentropy portion. In some embodiments of the present invention depictedin FIG. 30, the first entropy-slice header 1024 may be constrained to belocated within 2p bits 1031 after k−p bits 1027 from the referencelocation 1021, the second entropy-slice header 1025 may be constrainedto be located within 2p bits 1032 after 2k−p bits 1028 from thereference location 1021, the second entropy-slice header 1026 may beconstrained to be located within 2p bits 1033 after 3k−p bits 1029 fromthe reference location 1021. In these embodiments, an entropy decoderassigned to decode entropy slice N may begin searching for thecorresponding entropy-slice header after Nk−p bits from the referencelocation and may terminate the search after identifying theentropy-slice header or after searching 2p bits.

Some embodiments of the present invention may be described in relationto FIG. 31. In these embodiments, an entropy decoder may receive 1050 anentropy-slice number indicating the number of the entropy slice in thecurrent reconstruction block to entropy decode. The entropy decoder maydetermine 1052 the entropy-slice-location information. In someembodiments of the present invention, the entropy-slice-locationinformation, also referred to as entropy-slice-location parameters, maybe signaled in the bitstream, and the decoder may determine 1052 theentropy-slice information by examining the bitstream. In alternativeembodiments, the entropy-slice-location information may not be signaledin the bitstream, but may be determined 1052, by the decoder, fromentropy-slice parameters, for example, a fixed number of bins allowed inany given entropy slice, a fixed number of bits allowed in any givenentropy slice and other entropy-slice parameters. In still alternativeembodiments of the present invention, the entropy-slice-locationinformation may be defined and determined 1052 by other normative means,for example, the information may be specified in a profile constraint, alevel constraint, an application constraint, or other constraint, or theinformation may be signaled as supplemental information or signaled byother out-of-bound means.

The entropy decoder may calculate 1054 an entropy-slice-search startlocation at before which, in the bitstream, the entropy-slice header isrestricted from having been written by the encoder. In some embodimentsof the present invention, the entropy-slice-search start location may becalculated 1054 using an offset value and a range value determined fromthe entropy-slice-location information. In alternative embodiments ofthe present invention, the entropy-slice-search start location may becalculated 1054 using an offset value determined from theentropy-slice-location information. The entropy decoder may advance1056, in the bitstream, to the entropy-slice-search start location, andmay examine 1058 the bitstream for an entropy-slice header. In someembodiments of the present invention, an entropy-slice header may beindicated by a start code.

Some embodiments of the present invention may be described in relationto FIG. 32. In these embodiments, an entropy decoder may receive 1070 anentropy-slice number indicating the number of the entropy slice in thecurrent reconstruction block to entropy decode. The entropy decoder maydetermine 1072 the entropy-slice-location information. In someembodiments of the present invention, the entropy-slice-locationinformation, also referred to as entropy-slice-location parameters, maybe signaled in the bitstream, and the decoder may determine 1072 theentropy-slice information by examining the bitstream. In alternativeembodiments, the entropy-slice-location information may not be signaledin the bitstream, but may be determined 1072, by the decoder, fromentropy-slice parameters, for example, a fixed number of bins allowed inany given entropy slice, a fixed number of bits allowed in any givenentropy slice and other entropy-slice parameters. In still alternativeembodiments of the present invention, the entropy-slice-locationinformation may be defined and determined 1072 by other normative means,for example, the information may be specified in a profile constraint, alevel constraint, an application constraint, or other constraint, or theinformation may be signaled as supplemental information or signaled byother out-of-bound means.

The entropy decoder may calculate 1074 an entropy-slice-search startlocation before which, in the bitstream, the entropy-slice header isrestricted from having been written by the encoder. In some embodimentsof the present invention, the entropy-slice-search start location may becalculated 1074 using an offset value and a range value determined fromthe entropy-slice-location information. In alternative embodiments ofthe present invention, the entropy-slice-search start location may becalculated 1074 using an offset value determined from theentropy-slice-location information. The entropy decoder may advance1076, in the bitstream, to the entropy-slice-search start location andmay examine 1078 the bitstream for an entropy-slice header. In someembodiments of the present invention, an entropy-slice header may beindicated by a start code.

The bits, in the bitstream, may be examined 1078 in sequence starting atthe entropy-slice-search start location. If 1080 an entropy-slice headeris identified 1081, then the entropy decoder may entropy decode 1082 theentropy slice associated with the identified entropy-slice header. If1080 an entropy-slice header is not identified 1083, then the entropydecoder may terminate 1084 the search. In some embodiments, the entropydecoder may indicate an error when no entropy-slice header is identified1083.

Some embodiments of the present invention may be described in relationto FIG. 33. In these embodiments, an entropy decoder may receive 1100 anentropy-slice number indicating the number of the entropy slice, in thecurrent reconstruction, block to entropy decode. The entropy decoder maydetermine 1102 the entropy-slice-location information. In someembodiments of the present invention, the entropy-slice-locationinformation, also referred to as entropy-slice-location parameters, maybe signaled in the bitstream, and the decoder may determine 1102 theentropy-slice information by examining the bitstream. In alternativeembodiments, the entropy-slice-location information may not be signaledin the bitstream, but may be determined 1102, by the decoder, fromentropy-slice parameters, for example, a fixed number of bins allowed inany given entropy slice, a fixed number of bits allowed in any givenentropy slice and other entropy-slice parameters. In still alternativeembodiments of the present invention, the entropy-slice-locationinformation may be defined and determined 1102 by other normative means,for example, the information may be specified in a profile constraint, alevel constraint, an application constraint, or other constraint, or theinformation may be signaled as supplemental information or signaled byother out-of-bound means.

The entropy decoder may calculate 1104 an entropy-slice-search startlocation before which, in the bitstream, the entropy-slice header isrestricted from having been written by the encoder. In some embodimentsof the present invention, the entropy-slice-search start location may becalculated 1104 using an offset value and a range value determined fromthe entropy-slice-location information. In alternative embodiments ofthe present invention, the entropy-slice-search start location may becalculated 1104 using an offset value determined from theentropy-slice-location information. The entropy decoder may advance1106, in the bitstream, to the entropy-slice-search start location andmay examine 1108 the bitstream for an entropy-slice header. In someembodiments of the present invention, an entropy-slice header may beindicated by a start code.

The bits, in the bitstream, may be examined 1108 in sequence starting atthe entropy-slice-search start location. If 1110 an entropy-slice headeris identified 1111, then the entropy decoder may entropy decoder 1112the entropy slice associated with the identified entropy-slice header.If 1110 an entropy-slice header is not identified 1113, then if 1114 asearch criterion is satisfied 1115, the entropy decoder may terminate1116. The search criterion may provide a standard by which adetermination may be made as to whether, or not, valid locations for thestart of entropy-slice header remain to be searched. In some embodiments(not shown), a search criterion may be satisfied if valid locationsremain to be examined. In alternative embodiments, a search criterionmay be satisfied if there are no valid locations remaining to beexamined 1115, and the search may terminate 1116. In some embodiments,the entropy decoder may indicate an error when no entropy-slice headeris identified 1115. If 1114 the search criterion is not satisfied 1117,the examination 1108 of the bitstream may continue after advancing 1118,in the bitstream to the next search location.

In some embodiments of the present invention, the search criterion maybe related to a range value, for example, the location of the start ofan entropy-slice header may be restricted to a range of 2p bits centeredat Nk, where k denotes the offset value, p denotes the range value and Nis the entropy slice number within a reconstruction slice. In theseembodiments, the location of the start of the entropy-slice headerassociated with entropy slice N may be restricted to the range Nk−p toNk+p. In some embodiments, the search criterion may be related to arestriction, or restrictions, on the size of an entropy slice. In someembodiments, the search criterion may be related to a combination ofrestrictions.

In some embodiments of the present invention, an encoder may pad anentropy slice in order to meet a restriction on the location of the nextentropy-slice header.

In some embodiments of the present invention, an encoder may terminatean entropy slice prior to other entropy-slice size restrictions beingmet in order to meet a restriction on the location of the nextentropy-slice header.

In some embodiments of the present invention, when the last entropyslice within a reconstruction slice does not contain the number of bits(or bytes, in a byte-aligned embodiment) necessary to satisfy theconstraint on the location of the next entropy-slice header, an encodermay pad the last entropy slice within the reconstruction slice tosatisfy the constraint on the location of the next entropy-slice header.

In alternative embodiments, an entropy-slice header may comprise alast-entropy-slice flag, wherein the value of the last-entropy-sliceflag may indicate whether or not the entropy slice associated with theentropy-slice header is the last entropy slice in a reconstructionslice. In some embodiments, a last-entropy-slice flag value of zero maybe associated with the last entropy slice. In alternative embodiments, alast-entropy-slice flag value of one may be associated with the lastentropy slice. In some embodiments, when the value of thelast-entropy-slice flag indicates that the entropy slice is the lastentropy slice in a reconstruction slice, then the subsequententropy-slice header may be located immediately following the currententropy slice without padding.

Table 7 shows exemplary syntax and semantics for signaling alast-entropy-slice flag, referred to as a “next_entropy_slice_flag.” Inan exemplary embodiment comprising the exemplary syntax and semanticsshown in Table 7, the “next_entropy_slice_flag” flag signals if thereare additional entropy slices for a current reconstruction slice. If the“next_entropy_slice_flag” flag indicates that there are no additionalentropy slices for the current reconstruction slice, then the locationof the next entropy-slice header in the bitstream may not be constrainedby the entropy-slice-location parameters.

In some embodiments of the present invention, the location ofentropy-slice headers may be organized in a tree format with the rootnode pointing to an entropy-slice header location. In some embodiments,the entropy-slice header location pointed to by the root node may berelative. In alternative embodiments, the entropy-slice header locationpointed to by the root node may be absolute. The remaining nodes of thetree may contain offset distances with respect to their parent node. Thetree may be designed according to a design constraint, for example, toreduce an average time for determining entropy-slice header location, tobound a worst-case time required for determining entropy-slice headerlocation, to signal a preferred order of entropy slice decoding, tominimize a storage cost for the tree and other design constraints. Insome embodiments, the number of children of each node in the tree may becontrolled based on a desired level of parallelism in entropy-sliceheader location determination.

TABLE 7 Exemplary Syntax Table for Last-Entropy-Slice Flag C Descriptorslice-header( ) {   entropy_slice_flag 2 u(1)   next_entropy _slice_flag2 ue(v)   if (entropy_slice_flag) {    first_mb_in_slice 2 ue(v)    if(entropy_coding_mode_flag && slice_    type != I &&slice_type !=SI )    cabac_init_idc 2 ue(v)    }   }  else {   a regular slice header . .. . . . . .  } }

In some embodiments of the present invention, the context models may bereset within an entropy slice whenever a context-model-reset conditionis met. In some of these embodiments, the values to which the contextmodels may be reset may be based on the context model of a neighboringelementary unit within the entropy slice, and if the neighboringelementary unit is not within the entropy slice, then default values maybe used. In alternative embodiments, the context models may be reset todefault values. In yet alternative embodiments, the context models maybe reset based on a context model whose identifier may be signaledwithin the bitstream, the identifier indicating one of a plurality ofpredefined context models. A predefined context model may depend on one,or more, parameters in the bitstream. In exemplary embodiments, thecontext models may be reset based on a signaled “cabac_init_idc” value,within the bitstream, indicating one of a plurality of predefinedcontext models.

In some embodiments, a context table may be used to initialize aplurality of context models, wherein a context table refers to a set ofcontext models. In some embodiments, the set of context models in acontext table may undergo adaptation based on one, or more, parametersin the bitstream, for example, a quantization parameter, a slice typeparameter or other parameter.

In one exemplary embodiment illustrated in FIG. 34, the context modelsmay be reset, within an entropy slice, when a current macroblock is thefirst macroblock in a row, in addition to being reset at the startingmacroblock in an entropy slice. FIG. 34 depicts an exemplaryreconstruction slice 1200 containing 48 macroblocks 1208-1255partitioned into three entropy slices: entropy slice “0” (shown incross-hatch) 1202, entropy slice “1” (shown in white) 1204 and entropyslice “2” (shown in dot-hatch) 1206. Entropy slice “0” 1202 contains 15macroblocks 1208-1222. Entropy slice “1” 1204 contains 17 macroblocks1223-1239, and entropy slice “2” 1206 contains 16 macroblocks 1240-1255.The macroblocks at which the context models may be reset are indicatedwith a thick black edge 1260-1266 and are those macroblocks 1208, 1223,1240 at the start of each entropy slice and the first macroblock in eachrow 1216, 1224, 1232, 1240, 1248.

The elementary unit, for example, the macroblock, at the start of anentropy slice may be referred to as the slice-start elementary unit. Forexample, for the entropy slices 1202, 1204, 1206 in the exemplaryreconstruction slice 1200 in FIG. 34, the respective slice-startelementary units are 1208, 1223 and 1240. An elementary unit that is thefirst elementary unit in a row in an entropy slice may be referred to asa row-start elementary unit, for example, macroblocks 1208, 1216, 1224,1232, 1240 and 1248 in FIG. 34.

In some embodiments, the context models may be reset based on thecontext models of a neighboring macroblock if the neighboring macroblockis within the entropy slice and default values if the neighboringmacroblock is not within the entropy slice. For example, the contextmodels may be reset based on the context models of the macroblock abovethe current macroblock if the macroblock above the current macroblock isin the same entropy slice, but set to default values if the macroblockabove the current macroblock is not in the same entropy slice.

In another exemplary embodiment, the context models may be reset, withinan entropy slice, when a current elementary unit is the first elementaryunit in a row. In alternative embodiments, the context-model-resetcondition may be based on other criteria, for example, the number ofbins processed within the entropy slice, the number of bits processedwithin the slice, the spatial location of the current elementary unitand other criterion.

In some embodiments of the present invention, a context-model-reset flagmay be used to indicate whether or not the context models may be resetwithin an entropy slice whenever a context-model-reset condition is met.In some embodiments, the context-model-reset flag may be in theentropy-slice header. In alternative embodiments, thecontext-model-reset flag may be in the reconstruction-slice header. Insome embodiments, the context-model-reset flag may be a binary flag, andthe context-model-reset condition may be a default condition. Inalternative embodiments, the context-model-reset flag may by amulti-valued flag further indicating the context-model-reset condition.

In one exemplary embodiment comprising context-adaptive coding, forexample, CABAC coding, CAV2V coding and other context-adaptive coding,an “lcu_row_cabac_init_flag” flag may signal if entropy decoding may beinitialized at the start of the largest coding unit (LCU) row. In someembodiments, an LCU is a generalization of the macroblock concept usedin H.264 to high efficiency video coding (HEVC), and a picture isdivided into slices, wherein a slice is made up of a sequence of LCUs.In alternative embodiments, an LCU is the largest block of pixel valuelocations that may be represented with a single, transmitted mode value.In alternative embodiments, an LCU is the largest block of pixel valuelocations that may be represented with a single, transmitted predictionmode value. In some embodiments of the present invention, an“lcu_row_cabac_init_flag” flag value of “1” may signal that the entropycoding context is reset. An entropy coding context may represent the setof all context models associated with an entropy coder. In someembodiments of the present invention, an “lcu_row_cabac_init_flag” flagvalue of “1” may signal that the entropy coding context is reset and theadaptive scanning is reset. Adaptive scanning may refer to a process inwhich a codec adapts a scan ordering of transform coefficients based onpreviously transmitted transform coefficient values. Section 7.6.1 inthe JCTVC document JCTVC-B205_draft005, which is hereby incorporated byreference herein in its entirety, outlines an example where adaptivescanning chooses between two distinct scanning orders based on thesignificant coefficients in the neighbor. In one embodiment, theadaptive scanning may be reset at the start of every LCU row by choosinga pre-defined scanning order. In one embodiment, the scan ordering isdetermined by generating a coefficient significance map, and thetransform coefficient values corresponding to coefficient significancevalues larger than a pre-determined value may be transmitted prior tothe transform coefficient values corresponding to coefficientsignificance values less than or equal to the pre-determined value. Inone embodiment, the coefficient significance values that correspond totransform coefficient values that are greater than a pre-determinedvalue may subsequently be increased. In an alternative embodiment, thecoefficient significance values that correspond to transform coefficientvalues that are less than or equal to a pre-determined value maysubsequently be decreased. The adaptive scanning process may be reset bysetting the coefficient significant map to a pre-defined value. In someembodiments, the default value, assumed when the flag is not sent, forthe “lcu_row_cabac_init_flag” flag may be “0.” An“lcu_row_cabac_init_idc_flag” flag may signal if cabac_init_idc valueswill be transmitted at the start of each LCU row. In some embodiments,when the value of the “lcu_row_cabac_init_idc_flag” flag is “1” valueswill be transmitted at the start of each LCU row. In some embodiments,the default value, assumed when the flag is not sent, for the“lcu_row_cabac_init_idc_flag” flag may be “0.” In some embodiments, a“cabac_init_idc_present_flag” flag may signal if a cabac_init_idc valueis transmitted for the LCU. In some embodiments, when a cabac_init_idcvalue is not transmitted for the LCU then the entropy coding context isreset using the preceding value for cabac_init_idc in the bit-stream. Insome embodiments of the present invention, “lcu_row_cabac_init_flag” and“lcu_row_cabac_init_idc_flag” may be signaled in a regular slice header,for example, when the value of “entropy_slice_flag” is “0”. Table 8 andTable 9 show exemplary syntax for these embodiments. Table 8 showsexemplary slice header syntax, and Table 9 shows exemplary slice datasyntax.

TABLE 8 Exemplary Syntax Table for Signaling the Initialization ofEntropy Coding at the Start of the LCU Row C Descriptor slice_header( ){   entropy_slice_flag 2 u(1)   if (entropy_slice_flag) {   first_lcu_in_slice 2 ue(v)    if (entropy_coding_mode_flag) {    lcu_row_cabac_init_flag 1 u(1)     if( lcu_row_cabac_init-flag ){     lcu_row_cabac_init_idc_flag 1 u(1)     }    }    if(entropy_coding_mode_flag &&    slice_type !=I) {     cabac_init_idc 2ue(v)    }   }  else {   lcu_row_cabac_init_flag 1 u(1)   if(lcu_row_cabac_init_flag ){    lcu_row_cabac_init_idc_flag 1 u(1)   }   aregular slice header . . . . . . . .  } }

TABLE 9 Exemplary Syntax Table for Signaling the Initial Context for theLCU C Descriptor coding_unit( x0, y0, currCodingUnitSize ) {   if (x0==0&& currCodingUnitSize==   MaxCodingUnitSize &&   lcu_row_cabac_init_idc_flag==true && lcu_    id!=first_lcu_in_slice){     cabac_init_idc_present_flag 1 u(1)     if(cabac_init_idc_present_flag )      cabac_init_idc 2 ue(v)   }  a regularcoding unit . . . }

In another exemplary embodiment comprising context-adaptive coding, forexample, CABAC coding, CAV2V coding and other context-adaptive coding,an “mb_row_cabac_init_flag” flag may signal if entropy decoding may beinitialized at the first macroblock in a row. In some embodiments of thepresent invention, an “mb_row_cabac_init_flag” flag value of “1” maysignal that the entropy coding context is reset at the start of eachmacroblock row. In alternative embodiments of the present invention, an“mb_row_cabac_init_flag” flag value of “1” may signal that the entropycoding context is reset and the adaptive scanning is reset at the startof each macroblock row. In some embodiments, the default value, assumedwhen the flag is not sent, for the “mb_row_cabac_init_flag” flag may be“0.” An “mb_row_cabac_init_idc_flag” flag may signal if cabac_init_idcvalues will be transmitted at the start of each macroblock row. In someembodiments, when the value of the “mb_row_cabac_init_idc_flag” flag is“1” values will be transmitted at the start of each macroblock row. Insome embodiments, the default value, assumed when the flag is not sent,for the “mb_row_cabac_init_idc_flag” flag may be “0.” In someembodiments, a “cabac_init_idc_present_flag” flag may signal if acabac_init_idc value is transmitted for the macroblock. In someembodiments, when a cabac_init_idc value is not transmitted for themacroblock, then the entropy coding context is reset using the precedingvalue for cabac_init_idc in the bit-stream. In some embodiments of thepresent invention, the “mb_row_cabac_init_flag” flag and the“mb_row_cabac_init_idc_flag” flag may be signaled in a regular sliceheader, for example, when the value of “entropy_slice_flag” is “0”.Table 10 and Table 11 show exemplary syntax for these embodiments. Table10 shows exemplary slice header syntax, and Table 11 shows exemplaryslice data syntax.

TABLE 10 Exemplary Syntax Table for Signaling the Initialization ofEntropy Coding at the Start of the Macroblock Row C Descriptorslice_header( ) {   entropy_slice_flag 2 u(1)   if (entropy_slice_flag){    first_mb_in_slice 2 ue(v)    if (entropy_coding_mode_flag) {    mb_row_cabac_init_flag 1 u(1)     if( mb_row_cabac_init_flag ){      mb_row_cabac_init_idc_flag 1 u(1)     }    }    if(entropy_coding_mode_flag &&    slice_type != I) {     cabac_init_idc 2ue(v)    }   }  else {   mb_row_cabac_init_flag 1 u(1)   if(mb_row_cabac_init_flag ){    mb_row_cabac_init_idc_flag 1 u(1)   }   aregular slice header . . . . . . . .  } }

TABLE 11 Exemplary Syntax Table for Signaling the Initial Context forthe Macroblock C Descriptor coding_unit( x0, y0, currCodingUnitSize ) {  if (x0==0 && currCodingUnitSize==   MaxCodingUnitSize &&   mb_row_cabac_init_idc_flag==true && mb_id!=    first_mb_in_slice) {    cabac_init_idc_present_flag 1 u(1)     if(cabac_init_idc_present_flag )      cabac_init_idc 2 ue(v)   }  a regularcoding unit . . . }

In some embodiments of the present invention, the locations, in abitstream, of the entropy slices may be signaled in the bitstream. Insome embodiments, a flag may be used to signal that the locations, inthe bitstream, of the entropy slices are going to be signaled in thebitstream. Some exemplary embodiments may comprise an“entropy_slice_locations_flag” that if “true” may indicate that thelocations, in the bitstream, of the entropy-slice headers are going tobe signaled in the bitstream. In some embodiments, the location data maybe differentially encoded. In some embodiments, the location data may besent in each reconstruction slice. In alternative embodiments, thelocation data may be sent once per picture.

In some embodiments of the present invention, the locations, in abitstream, of the rows may be signaled in the bitstream. In someembodiments, a flag may be used to signal that the location, in thebitstream, of the first LCU in each row is going to be signaled in thebitstream. Some exemplary embodiments may comprise an“lcu_row_location_flag” that if “true” may indicate that the location,in the bitstream, of the first LCU in each row is going to be signaledin the bitstream. In some embodiments, the location data may bedifferentially encoded. In some embodiments, the location data may besent in each entropy slice. In alternative embodiments, the locationdata may be sent once per reconstruction slice.

Table 12 shows exemplary syntax for signaling the locations, in thebitstream, of the rows and the entropy slices. For this exemplarysyntax, the semantics are:

-   -   “entropy_slice_locations_flag” signals if entropy slice header        location is transmitted. If the value of        “entropy_slice_locations_flag” is set to “1”, then the entropy        slice header location is transmitted, otherwise it is not        transmitted. The default value for the        “entropy_slice_locations_flag” is “0”.    -   “num_of_entropy_slice_minus1” signals the number of entropy        slices in the reconstruction slice minus 1.    -   “entropy_slice_offset [i]” indicates the offset of the i^(th)        entropy slice from the previous entropy slice.    -   “lcu_row_locations_flag” signals if LCU row location information        is being transmitted or not. If the value of        “lcu_row_locations_flag” is “1”, then the LCU row location        information is transmitted, otherwise it is not transmitted. The        default value for “lcu_row_locations_flag” is “0”.    -   “num_of_lcu_rows_minus1” signals the number of LCU rows in the        entropy slice minus 1.    -   “lcu_row_offset [i]” indicates the offset of the i^(th) LCU row        from the previous LCU row.

TABLE 12 Exemplary Syntax Table for Signaling the Locations, in theBitstream, of the First LCU in a Row C Descriptor slice header( ) { entropy_slice_flag 2 u(1)   if (entropy_slice_flag){   first_lcu_in_slice 2 ue(v)    lcu_row_cabac_init_flag 1 u(1)    if(lcu_row_cabac_init_flag ){      lcu_row_cabac_init_idc_flag 1 u(1)     lcu_row_locations_flag 1 u(1)      if (lcu_row_locations_flag) {      lcu_row_locations ( )      }     }    if( entropy_coding_mode_flag&&    slice_type !=I) {      cabac_init_idc 2 ue(v)    }   }  else {  entropy_slice_locations_flag 1 u(1)   if(entropy_slice_locations_flag) {    entropy_slice_locations( )   }  lcu_row_cabac_init_flag 1 u(1)   if( lcurowcabac_initflag ) {    lcu_row_cabac_init_idc_flag 1 u(1)    lcu_row_locations_flag 1 u(1)   if (lcu_row_locations_flag) {     lcu_row_ locations ( )    }   }   aregular slice header . . . . . . . .  } } entropy_slice_locations ( ) { num_entropy_slices_minus1 2 ue(v)  for (i=0; i<num_of_entropy_slices_minus1; i++)   entropy_slice_offset[i] 2 ue(v) }lcu_row_ locations( ) {  num_of_lcu_rows_minus1 2 ue(v)  for (i=0;i<num_of_lcu_rows_minus1_slice; i++) {   lcu_row_offset[i] 2 ue(v)  } }

The efficient transmission of residual data from an encoder to a decodermay be accomplished by signaling the location of zero-valued transformcoefficients and the level values of the non-zero transform coefficientsfor an elementary unit, for example, a macroblock. Many coding systemsmay attempt to locate the zero-valued transform coefficients at the endof the residual data for the elementary unit, thereby allowing the useof an “end-of-block” code after the last significant transformcoefficient to efficiently signal that the remaining transformcoefficient values are zero.

Some coding systems may track the locations of zero-valued transformcoefficients in the residual data previously transmitted for apreviously processed elementary unit, which may allow the locations withprevious zero-valued transform coefficients to be transmitted last insubsequent residual data. Alternatively, some coding systems may trackthe locations of non-zero-valued transform coefficients in the residualdata previously transmitted. While this may improve coding efficiency,it makes it necessary to completely decode previous residual data inorder to decode current residual data due to the fact that the coding ofresidual data uses context models, also referred to as probabilitymodels, which are determined by a transform coefficient identifier thatmay only be determined with the knowledge of the locations that areidentified to be transmitted at the end of the residual data.

For example, if scanning adaptation has generated a scanning order of:S={coeff₀,coeff₁,coeff₀₁, . . . } for the entropy coding processassociated with a current elementary unit, where coeff_(i) denotes theith transform coefficient, then the context, which may be denoted ctxt₀,corresponding to coeff₀ needs to be fetched for coding transformcoefficient coeff₀. Next the context ctxt₁₀, corresponding to coeff₁₀needs to be fetched for coding transform coefficient coeff₁₀, and so on.Thus, a temporal ordering on the coding of the elementary units may beenforced due to the necessity of knowing the scan orderS={coeff₀,coeff₁, coeff₀₁, . . . }, which cannot be obtained untilprevious elementary units have been coded.

In some embodiments of the present invention, in order to allow parallelcoding of entropy slices, adaptive scanning may be reset to an entropyslice default scan order at the slice-start elementary unit of eachentropy slice, thereby allowing separate entropy slices to be coded inparallel.

In some embodiments of the present invention, a scan order of anadaptive scan calculation may be set to a known, also referred to as arow default, scan order at the row-start elementary unit of each LCU rowwithin an entropy slice.

In alternative embodiments of the present invention, the blocktransform-coefficient scanning order and the corresponding contextmodel, also referred as context, which may be fetched for coding atransform coefficient may be decoupled, thereby allowing parallelcoding. In these embodiments, a transform coefficient located at a firstlocation in the bitstream may be associated, based on its locationrelative to the other transform coefficients in the bitstream, with acorrespondingly located context in a context fetch order. In theseembodiments, a context fetch order, which may be denotedF={ctxt_(A),ctxt_(B),ctxt_(C), . . . }, where ctxt_(•) denotes a contextthat is not associated with a transform-coefficient location in thetransform domain, but rather is associated with the relative location ofthe transform coefficient in the bitstream, may be predefined. Thus, foran exemplary transform-coefficient scan order S={coeff₀,coeff₁,coeff₀₁,. . . }, the coding process may code coeff₀ with ctxt_(A), coeff₁₀ withctxt_(B), coeff₁ with ctxt_(C) and so on. In these embodiments, theentropy-coding process may operate independently of the scanning order.Some encoder embodiments may be described in relation to FIG. 35. Anencoder may fetch 1280 the next transform coefficient to be encoded andmay fetch 1282 the next context, from a predefined fetch list ofcontexts. The fetched transform coefficient may be entropy encoded 1284using the fetched context, and a determination 1286 may be made as towhether or not there are significant transform coefficients remaining toencode. If there are 1287 significant transform coefficients remainingto be encoded, the next significant transform coefficient may be fetched1280, and the process may continue. If there are not 1289, then theprocess may terminate 1290. Some decoder embodiments may be described inrelation to FIG. 36. A decoder may fetch 1300 the next context andentropy decode 1302 the next significant transform coefficient from thebitstream using the fetched context. The decoded transform coefficientmay be stored 1304, and a determination 1306 may be made as to whetheror not there are remaining significant transform coefficients to bedecoded. If there are 1307, then the next context may be fetched 1300,and the process may continue. If there are not 1309, then areconstruction process may reverse 1310 the adaptive scanning beforefurther processing.

In alternative embodiments of the present invention, a coefficientscanning order may be restricted to a subset of all possible scanningcombinations and may be explicitly signaled. At the start of an entropyslice, the scanning order may be set to a signaled scanning order. Insome embodiments, the scanning order may be signaled as a normativesyntax. In alternative embodiments, the scanning order may be signaledwith a non-normative message, for example, an SEI message or othernon-normative message.

In alternative embodiments of the present invention, a coefficientscanning order may be restricted to a subset of all possible scanningcombinations and may be explicitly signaled. At the start of an LCU rowin an entropy slice, the scanning order may be set to a signaledscanning order. In some embodiments, the scanning order may be signaledas a normative syntax. In alternative embodiments, the scanning ordermay be signaled with a non-normative message, for example, an SEImessage or other non-normative message.

In yet alternative embodiments of the present invention, at thebeginning of an entropy slice, the coefficient scanning order may be setto the scanning order of a previously decoded elementary unit. In someembodiments, the scanning order may be set to the scanning order used inthe elementary unit above. In alternative embodiments, the scanningorder may be set to the scanning order used in the elementary unit aboveand to the right.

In yet alternative embodiments of the present invention, at thebeginning of an LCU row in an entropy slice, the coefficient scanningorder may be set to the scanning order of a previously decodedelementary unit. In some embodiments, the scanning order may be set tothe scanning order used in the elementary unit above. In alternativeembodiments, the scanning order may be set to the scanning order used inthe elementary unit above and to the right.

Referring to FIG. 42, in some embodiments of the present invention, aninitialization method for P-slices may be applied to forward-predictedB-slices, which may result in a higher compression efficiency due to thegreater degrees of freedom afforded to B-slices and the multi-hypothesisnature of B-predictions. The reference slices used in aforward-predicted B-slice are always from temporally earlierframes/pictures as distinguished from a regular B-slice wherein areference may be chosen from temporally future and/or pastframes/pictures. Thus, a forward-predicted B-slice may comprise residualdata with statistical characteristics differing from those of a regularB-slice. As illustrated in FIG. 42, the technique may receive B-slices,P-slices, and I-slices and based upon the type of slice received, aninitialization technique is selected. In addition, in the case of aforward-predicted B-slice the initialization technique for the P-sliceis used.

According to one aspect of the present invention, an initial probabilitydistribution used to initialize an entropy coder may be generated bytraining for forward-predicted B frames only. According to anotheraspect of the present invention, initialization of the context may beadapted based on the quantization parameter, which may be denoted QP,used to code the current video data.

In some embodiments of the present invention, an encoder mayalternatively apply an initialization method for P-slices toforward-predicted B-slices and may signal the occurrence of thealternation. In some embodiments of the present invention, the signalingmay be explicit. In alternative embodiments of the present invention,the signaling may be implicit. In some embodiments of the presentinvention comprising explicit signaling, a flag may be sent to thedecoder whenever a P-slice is replaced with a forward-predicted B-slice.In some of these embodiments, the flag may be signaled as a normativesyntax. In alternative embodiments, the flag may be signaled within anon-normative message, for example, an SEI message or othernon-normative message.

Referring to FIG. 40, in some embodiments of the present invention, aninitialization method for P-slices may be applied to uni-predictedB-slices, which may result in a higher compression efficiency due to thegreater degrees of freedom afforded to B-slices. The reference slicesused in a uni-predicted B-slice are a portion of either temporallyearlier frames/pictures or temporally later frames/pictures. Thus, auni-predicted B-slice may comprise residual data with statisticalcharacteristics different from those of a bi-directional B-slice.Temporally may refer to the display order of the decodedpictures/frames. As illustrated in FIG. 40, the technique may receiveB-slices, P-slices, and I-slices and based upon the type of slicereceived, an initialization technique is selected. In addition, in thecase of a uni-predicted B-slice the initialization technique for theP-slice is used.

Referring to FIG. 41, in some embodiments of the present invention, aforward predicted B-slice may be initialized in a manner different thana backward predicted B-slice and/or a bi-directional predicted B-slice,which, which may result in a higher compression efficiency due to thedifferent degrees of freedom afforded to B-slices. The reference slicesused in a forward predicted B-slice are a portion of temporally earlierframes/pictures. Thus, a forward predicted B-slice may comprise residualdata with statistical characteristics different from those of a backwardand/or bi-directional B-slice. Temporally may refer to the display orderof the decoded pictures/frames. As illustrated in FIG. 41, the techniquemay receive B-slices, P-slices, and I-slices and based upon the type ofslice received, an initialization technique is selected. In addition, inthe case of a forward-predicted B-slice an initialization techniquedifferent from the B-slices, P-slices, and I-slices may be used.

The initialization method may consist of setting values of an entropycoder that are necessary for operation of the entropy coder. Forexample, a first probability estimate may be set for an entropy coderthat uses probability estimates for coding data, such as in anarithmetic coder. The initialization method may use a initializationtechnique to determine the values. In one embodiment, a firstinitialization method corresponds to using a first table of precomputedvalues to set the values. Similarly, a second initialization methodcorresponds to using a second table of precomputed values to set thevalues. In another embodiment, a first initialization method uses afirst table of precomputed values that are designed for frames that usemore than one prediction between frames to set the values, where theframe(s) used for prediction both temporally preceed and proceed thecurrent frame when ordered in display order. A second initializationmethod uses a second table of precomputed values that are designed fromframes that use more than one prediction between frames to set thevalues, where the frames used for prediction temporally precede ortemporally proceed, but do not both temporally precede and temporallyproceed, the current frame when ordered in display order. A thirdinitialization method uses a third table of precomputed values that aredesigned for frames that use at most one prediction between frames toset the values. A fourth initialization method uses a fourth table ofprecomputed values that are designed for frames that do not useprediction between frames to set the values.

In one embodiment of the invention, RefPicList0 contains a list ofpreviously decoded frames that are displayed prior to display of thecurrent frame followed by a list of previously decoded frames that aredisplayed subsequent to display of the current frame and RefPicList1contains a list of previously decoded frames that are displayedsubsequent to the display of the current frame followed by a list ofpreviously decoded frames that are displayed prior to display of thecurrent frame. In this embodiment, condition (2) above is true for auni-directional B-slice since the number of previously decoded framesthat is displayed subsequent to the display of the current frame iszero, or the number of decoded frames that are displayed prior to thedisplay of the current frame is zero. In another embodiment of theinvention, PicOrderCnt denotes the display order of the decoded frames.In this embodiment, condition (3) above is true for a uni-directionalB-slice since the decoded frames are all displayed prior to the displayof the current frame or subsequent to the display of the current frame.

In some embodiments of the present invention comprising implicitsignaling, an occurrence of an initialization method for P-slicesapplied to forward-predicted B-slice, may be inferred at a decoder whenthe reference slices (frames/pictures) used in prediction are all pastslices (frames/pictures) based on the order in which the slices are tobe displayed. In some embodiments, the occurrence of a P-slice replacedby a uni-directional B-slice may be inferred when the followingconditions are true: (1) the reference picture list RefPicList1 has oneor more entries, (2) the reference picture list RefPicList1 andRefPicList0 contain the same set of pictures, and (3) all frames inreference picture list RefPicList1 and RefPiList0 have PicOrderCnt lessthan the PicOrderCnt of the current frame, where PicOrderCnt indicatesthe display order of the frames in ascending order. In some embodiments,the occurrence of a P-slice replaced by a uni-directional B-slice may beinferred when the following conditions are true: (1) the referencepicture list RefPicList1 has one or more entries, (2) the referencepicture list RefPicList1 and RefPicList0 contain the same set ofpictures, and (3) all frames in reference picture list RefPicList1 andRefPiList0 have PicOrderCnt greater than the PicOrderCnt of the currentframe, where PicOrderCnt indicates the display order of the frames inascending order. In some embodiments, the occurrence of a P-slicereplaced by a uni-directional B-slice may be inferred when the followingconditions are true: (1) the reference picture list RefPicList1 has oneor more entries, and (2) the first frame in the reference picture listRefPicList1 and the first frame in the RefPicList0 have PicOrderCnt less(or greater) than the PicOrderCnt of the current frame, wherePicOrderCnt indicates the display order of the frames in ascendingorder. In some embodiments, the occurrence of a P-slice replaced by auni-directional B-slice may be inferred when the following conditionsare true: (1) the reference picture list RefPicList1 has more than oneentry, and (2) the frames [0,N] in the reference picture listRefPicList1 and the frames [0,N] in the RefPicList0 have PicOrderCntless (or greater) than the PicOrderCnt of the current frame, wherePicOrderCnt indicates the display order of the frames in ascendingorder. In some embodiments, the occurrence of a P-slice replaced by auni-directional B-slice may be inferred when the following conditionsare true: (1) the reference picture list RefPicList1 has one or moreentries, (2) the first frame in the reference picture list RefPicList1is the same as the second frame in the reference picture listRefPicList0, (3) the second frame in the reference picture listRefPicList1 is the same as the first frame in the reference picture listRefPicList0, (4) the frames [0,N] in the reference picture listRefPicList1 and the frames [0,N] in the RefPicList0 have PicOrderCntless (or greater) than the PicOrderCnt of the current frame, wherePicOrderCnt indicates the display order of the frames in ascendingorder. In some embodiments the order in the RefPicList0 and RefPicList1need not be identical to contain the same set of pictures. In anexemplary embodiment, when the reference picture list RefPicList1 hasmore than one entry and RefPicList1 is identical to the referencepicture list RefPicLis0, then the first two entries RefPicList1[0] andRefPicList1[1] may be switched. N may refer to less than the totalnumber of frames/pictures in the reference picture list. The PicOrderCntmay also refer to a relative display order in a decoder picture buffer.

When the occurrence of a P-slice replaced by a forward-predicted B-sliceis indicated, the context for an entropy slice may be initialized usinga P-slice method.

Table 13 shows exemplary syntax for explicitly signaling that theinitial context of a B-slice is to be initialized using a P-slicemethod. In the exemplary embodiments associated with Table 11,“cabac_init_P_flag” is a flag that indicates, for B-slice entropyencoder initialization, whether a B-slice method or a P-slice methodshould be chosen. In some embodiments, if the value of the“cabac_init_P_flag” flag is “0,” then a B-slice method is chosen forinitialization, and if the value of the “cabac_init_P_flag” flag is “1,”then a P-slice method is chosen for initialization.

TABLE 13 Exemplary Syntax Table Showing Explicit Signaling of B-sliceInitialization Using a P-slice Method C Descriptor slice_header( ) {  entropy_slice_flag 2 u(1)   if (entropy_slice_flag) {     first_lcu_in_slice 2 ue(v)      lcu_row_cabac_init_flag 1 u(1)     if( lcu_row_cabac_init_flag ){       lcu_row_cabac_init_idc_flag 1u(1)      }      if( entropy_coding_mode_flag &&      slice_type != I) {      cabac_init_idc 2 ue(v)       if (slice_type==B_SLICE)       cabac_init_P_flag 1 u(1)      }   }  else {  lcu_row_cabac_init_flag 1 u(1)   if( lcu_row_cabac_init_flag ){    lcu_row_cabac_init_idc_flag 1 u(1)   }   first_lcu_in_slice 2 ue(v)  slice_type 2 ue(v)    Some elements of regular slice header . . . . ..    if( entropy_coding_mode_flag &&    slice_type != I) {    cabac_init_idc 2 ue(v)     if (slice_type==B_SLICE)       cabac_init_P_flag 1 u(1)     }    Remainder of regular sliceheader . . . . . . . .  } }

In some embodiments of the present invention, context initializationstates for an entropy slice may be based on the number of bins processedby an entropy coder. An entropy encoder may converge more quickly to thesource statistics when initialized correctly. Faster convergence mayresult in fewer bits being wasted and thus higher compressionefficiency. In some embodiments of the present invention, the number ofbins that may be transmitted may be estimated, and when the estimatednumber of bins meets a first criterion, then a first initializationmethod may be used. When the estimated number of bins does not meet thefirst criterion, a second initialization method may be used.

An exemplary embodiment of the present invention may be understood inrelation to FIG. 37. In these embodiments, the number of bins processedmay be estimated 1320. The estimated number of processed bins, denotedNbins, may be compared 1322 to a threshold value, denoted Tbins. As thenumber of bins processed increases the predictive accuracy of QP-basedcontext initialization may decrease. A higher predictive accuracy forcontext initialization may lead to better compression efficiency. If theestimated number of processed bins is 1324 greater than the thresholdvalue, than a single context initialization value may be chosen 1326. Ifthe estimated number processed bins is not 1328 greater than thethreshold value, then the context may be initialized adaptively 1330based on QP. The single context initialization value may be selectedbased on training and optimization of chosen metrics, for example,squared error, relative entropy and other distance metrics. An adaptiveQP-based initialization may be an affine adaptation of the formC_(A)*QP+C_(B), where C_(A) and C_(B) are constants. In someembodiments, the number of bins may be estimated based on the number ofbins processed in the previous slice. In alternative embodiments, thenumber of bins may be estimated based on the number of bins process inthe previous frame.

In some embodiments of the present invention described in relation toFIG. 38, which pictorially represents 1340 a range of number of binsprocessed, multiple, disjoint ranges (three shown 1342, 1344, 1346) ofnumber of bins processed may be determined and described in relation toa number of thresholds (two shown 1348, 1350), and the contextinitialization value may be selected based on within which of the ranges1342, 1344, 1346 the estimated number of bins processed falls, forexample, for three ranges 1342, 1344, 1346, when Nbins≦T_(min) 1342, thecontext may be initialized adaptively based on QP, when T_(min)<Nbins≦T₁1344, the context may be initialized to a first fixed context value andwhen T₁<Nbins 1346, the context may be initialized to a second,different, fixed context value.

Another alternative exemplary embodiment of the present invention may beunderstood in relation to FIG. 39. In this exemplary embodiment, thevalue of QP may be determined 1400 and examined 1402 in relation to athreshold value, denoted T_(QP). In general, as QP decreases the numberof bins processed may increase. If QP is not 1404 less than thatthreshold value, then the context may be initialized adaptively 1406based on QP. If the value of QP is 1408 less than the threshold value,then a single context initialization value may be chosen 1410. Thesingle context initialization value may be selected based on trainingand optimization of chosen metrics, for example, squared error, relativeentropy and other distance metrics.

In some embodiments of the present invention, multiple, disjoint rangesof QP may be determined, and the context initialization value may beselected based on within which of the ranges the QP value falls.

Table 14 shows a comparison of rate distortion performance for all-intracoding. The first comparison, shown in the two sub-columns of columnthree, is a comparison, using the H.264/AVC Joint Model (JM) software,version 13.0, between encoding using multiple slices, wherein entropydecoding and macroblock reconstruction for a slice does not depend onother slices, and encoding using no slices. On average, for the same bitrate, the quality is degraded by −0.3380 dB encoding using multipleslices over using no slices. On average, for the same quality level, thebit rate is increased by 7% by encoding using multiple slices over usingno slices.

The second comparison, shown in the two sub-columns of column four, is acomparison between encoding using one reconstruction slice partitioned,according to embodiments of the present invention, into multiple entropyslices (two rows of macroblocks per entropy slice) and encoding using JM13.0 with no slices. On average, for the same bit rate, the quality isdegraded by −0.0860 dB using one reconstruction slice with multipleentropy slices over encoding using no slices. On average, for the samequality level, the bit rate is increased by 1.83% by encoding using onereconstruction slice with multiple entropy slices over encoding using noslices.

TABLE 14 Comparison of rate distortion performance - all-intra encodingAll Intra Coding One reconstruction slice with JM 13.0 slices multipleentropy compared to slices compared to JM 13.0 no slices JM 13.0 noslices Reso- BD SNR BD Bit BD SNR BD Bit Sequence lution [dB] rate [%][dB] rate [%] BigShip 720 p −0.22 4.54 −0.08 1.61 City 720 p −0.28 4.03−0.06 0.84 Crew 720 p −0.42 11.67 −0.11 2.98 Night 720 p −0.38 5.64−0.06 0.91 ShuttleStart 720 p −0.39 9.12 −0.12 2.81 AVERAGE −0.3380 7.00−0.0860 1.83

Table 15 shows a comparison of rate distortion performance for IBBPcoding. The first comparison, shown in the two sub-columns of columnthree, is a comparison, using the H.264/AVC Joint Model (JM) software,version 13.0, between encoding using multiple slices, wherein entropydecoding and macroblock reconstruction for a slice does not depend onother slices, and encoding using no slices. On average, for the same bitrate, the quality is degraded by −0.5460 dB encoding using multipleslices. On average, for the same quality level, the bit rate isincreased by 21.41% by encoding using multiple slices over using noslices.

The second comparison, shown in the two sub-columns of column four, is acomparison between encoding using one reconstruction slice partitioned,according to embodiments of the present invention, into multiple entropyslices (two rows of macroblocks per entropy slice) and encoding using JM13.0 with no slices. On average, for the same bit rate, the quality isdegraded by −0.31 dB using one reconstruction slice with multipleentropy slices over encoding using no slices. On average, for the samequality level, the bit rate is increased by 11.45% by encoding using onereconstruction slice with multiple entropy slices over encoding using noslices.

TABLE 15 Comparison of rate distortion performance - IBBP encoding IBBPCoding One reconstruction slice with multiple entropy JM 13.0 slicescompared slices compared to to JM 13.0 no slices JM 13.0 no slices Reso-BD SNR BD Bit BD SNR BD Bit Sequence lution [dB] rate [%] [dB] rate [%]BigShip 720 p −0.45 19.34 −0.26 10.68 City 720 p −0.48 17.83 −0.22  7.24Crew 720 p −0.62 30.10 −0.33 14.93 Night 720 p −0.36 11.11 −0.19  5.5ShuttleStart 720 p −0.82 28.69 −0.55 18.89 AVERAGE −0.5460 21.41 −0.3111.45

Comparing the results, encoding using multiple entropy slices in onereconstruction slice provides a bit rate savings of 5.17% and 9.96% forall-intra and IBBP coding, respectively, over encoding using slices,wherein entropy decoding and macroblock reconstruction for a slice doesnot depend on other slices, although both allow for parallel decoding.

Table 16 shows a comparison of rate distortion performance for all-intraand IBBP coding. In this table, the comparison is a comparison betweenencoding using no slices and encoding using one reconstruction slicepartitioned into entropy slices, according to embodiments of the presentinvention, of maximum size 26 k bins per entropy slice. The firstcomparison, shown in the two sub-columns of column two, is a comparisonusing all-intra coding. On average, for the same bit rate, the qualityis degraded by −0.062 dB by encoding using a reconstruction slice withmultiple entropy slices. On average, for the same quality level, the bitrate is increased by 1.86% by encoding using a reconstruction slice withmultiple entropy slices. Thus, for all-intra coding using entropy slicesof maximum size 26 k bins per entropy slice, there is an average bitrate savings of approximately 0.64% over that of fixed entropy slicesizes of two rows of macroblocks.

The second comparison, shown in the two sub-columns of column three, isa comparison using IBBP coding. On average, for the same bit rate, thequality is degraded by −0.022 dB using one reconstruction slice withmultiple entropy slices over encoding using no slices. On average, forthe same quality level, the bit rate is increased by 0.787% by encodingusing one reconstruction slice with multiple entropy slices overencoding using no slices. Thus, for IBBP coding using entropy slices ofmaximum size 26 k bins per entropy slice, there is an average bit ratesavings of approximately 10.66% over that of fixed entropy slice sizesof two rows of macroblocks.

TABLE 16 Comparison of rate distortion performance - all-intra and IBBPencoding using entropy slices with less than 26k bins per entropy sliceEntropy Slice Compared to JM 15.1 No Slice. Experiment (1): 26k binsmaximum per entropy slice All Intra Coding IBBP Coding Sequence BD SNRBD Bit BD SNR BD Bit (720 p) [dB] rate [%] [dB] rate [%] BigShip −0.071.40 −0.02 0.70 City −0.07 1.02 −0.02 0.51 Crew −0.05 1.31 −0.03 1.25Night −0.07 1.00 −0.02 0.66 ShuttleStart −0.05 1.20 −0.03 −0.82 AVERAGE−0.062 1.187 −0.022 0.787

The use of entropy slices allows for parallel decoding, and encoderpartitioning of a reconstruction slice into entropy slices, wherein eachentropy slice is less than a maximum number of bins may provideconsiderable bit rate savings over entropy slices of a fixed number ofmacroblocks.

Although the charts and diagrams in the figures may show a specificorder of execution, it is understood that the order of execution maydiffer from that which is depicted. For example, the order of executionof the blocks may be changed relative to the shown order. Also, as afurther example, two or more blocks shown in succession in a figure maybe executed concurrently, or with partial concurrence. It is understoodby those with ordinary skill in the art that software, hardware and/orfirmware may be created by one of ordinary skill in the art to carry outthe various logical functions described herein.

Some embodiments of the present invention may comprise a computerprogram product comprising a computer-readable storage medium havinginstructions stored thereon/in which may be used to program a computingsystem to perform any of the features and methods described herein.Exemplary computer-readable storage media may include, but are notlimited to, flash memory devices, disk storage media, for example,floppy disks, optical disks, magneto-optical disks, Digital VersatileDiscs (DVDs), Compact Discs (CDs), micro-drives and other disk storagemedia, Read-Only Memory (ROMs), Programmable Read-Only Memory (PROMs),Erasable Programmable Read-Only Memory (EPROMS), Electrically ErasableProgrammable Read-Only Memory (EEPROMs), Random-Access Memory (RAMS),Video Random-Access Memory (VRAMs), Dynamic Random-Access Memory (DRAMs)and any type of media or device suitable for storing instructions and/ordata.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention in the use of such terms andexpressions of excluding equivalence of the features shown and describedor portions thereof, it being recognized that the scope of the inventionis defined and limited only by the claims which follow.

What is claimed is:
 1. A method for decoding a video frame of a videosequence, the method comprising: (a) receiving a slice in a videodecoder; (b) identifying a type of the slice as one of a groupconsisting of: a first slice type and a second slice type; (c) receivinga flag for determining an initialization method corresponding to theslice; (d) initializing, based on the received flag and the identifiedtype of the slice, a Context-Adaptive Binary Arithmetic Coding (CABAC)context associated with the slice using one of a group consisting of:(i) a first initialization method and (ii) a second initializationmethod; and (e) decoding the video frame using the type of the slice andone of the first initialization method and the second initializationmethod; wherein an initialization method, which initializes a CABACcontext associated with a B-slice type is a B-slice method, in case thata value of the received flap is equal to a first value, and aninitialization method which initializes the CABAC context associatedwith the B-slice type is a P-slice method, in case that the value of thereceived flap is equal to a second value.
 2. The method of claim 1,wherein the flag is provided in a slice header.